Every Concept, Page 2 of 11: Plain-Language Definitions

Design
Prototype testing
A research method in which people try an early, unfinished version of a product so a team can fix its design before building it.
Design
Proximity
The Gestalt principle that objects placed close together are seen as one group, and objects set further apart as separate groups.
AI & Engineering
Chain of Thought
Chain of thought is a prompting technique in which a language model writes its intermediate steps before answering, so each step can support the next.
Design
Chunking
Chunking is grouping separate items into one familiar unit, so that working memory stores one unit instead of many.
Psychology
Common Ground
Common ground is the knowledge and assumptions that people share and know they share, which speakers rely on and build up by checking they were understood.
AI & Engineering
Fine-Tuning
Continuing to train a model that already learned general patterns during pretraining on a smaller, task-specific dataset, so it adapts to a narrower job without starting from scratch.
Business
Lifetime Value
Lifetime value is the total profit a business expects to earn from one customer over the whole relationship, discounted to today's money.
Psychology
Nudge Theory
A change in how a choice is presented that predictably shifts what people pick, without banning any option or changing its cost.
Business
Precision
How closely repeated measurements of the same thing agree with each other; in classification, the share of positive predictions that are correct.
Psychology
Scarcity Principle
People value an option more, and act sooner, when it looks limited in quantity, time, or who can get it.
Design
Scenarios
A short story about a specific person using a product to reach a goal in a specific situation, written to find design needs and test tasks.
AI & Engineering
Self-Attention
The mechanism inside a Transformer that lets every element of a sequence weigh and combine information from every other element in that sequence.
Business
Survivorship Bias
A sampling error that comes from studying only the cases that survived a selection process and ignoring those that dropped out, so results look better than the full group.
Design
The Necessity of Choice
The fact that time, attention, and money are limited, so any person or team must choose what to do and what to leave undone.
Design
Visual Noise
Marks on a screen that draw attention without helping the task, so the important item stands out less and takes longer to find.
Product
Wireframing
Drawing a screen's layout as grey boxes and labels before visual design or code, so a team can agree on what goes where.
AI & Engineering
Bias-Variance Tradeoff
The pattern that a model's prediction error splits into bias from being too simple and variance from being too sensitive to its training sample, which move in opposite directions.
Business
Bounded Rationality
The idea that people decide with limited information, thinking capacity and time, so they search until an option is good enough instead of finding the best one.
Marketing
Brand Identity
The visual, verbal and behavioural signs a company chooses so that people recognise it and know what to expect.
Marketing
Consumer Psychology
The study of how people notice, judge, choose and use what they buy, including motives they cannot name.
Design
Design Tokens
Named values that store a design system's colours, type, spacing and motion once, so every platform reads the same decision from one source.
Psychology
Halo Effect
The tendency to let one good impression of a person, brand, or product shape how you judge their other, unrelated qualities.
Research
Journey mapping
A research method that lays out the steps one kind of person takes toward a goal, with what they do, think and feel at each step.
Research
Occam's Razor
Occam's razor is the rule that, between explanations fitting the same evidence equally well, the one assuming the fewest extra causes should be preferred until evidence says otherwise.
AI & Engineering
Reinforcement Learning from Human Feedback
Reinforcement Learning from Human Feedback (RLHF) trains a language model to produce the responses human raters prefer, using a reward model built from their comparisons.
Design
Signifiers
A signifier is a perceivable cue, such as a flat plate on a door or a raised edge on a button, that shows people which action is possible and where to take it.
Design
WCAG 2.1 AA
WCAG 2.1 AA is the conformance level at which a web page meets every Level A and Level AA success criterion of the W3C's Web Content Accessibility Guidelines 2.1.
Psychology
Authority Bias
The tendency to treat a statement or an order as more accurate or more binding because it comes from an authority figure, regardless of its content.
Psychology
Cognitive Dissonance
The discomfort of holding two conflicting beliefs, or acting against a belief, and the pull to make them consistent.
Psychology
Cognitive Load Theory
A theory that learning fails when a task asks working memory to hold more new items than it can, and that design should cut the extra demand.
Design
Leading
Leading is the vertical space between lines of text, named after the lead strips printers set between lines of metal type, and it controls how dense and readable a paragraph feels.
Design
Mode Error
An action that is right for the mode a person believes a system is in, but wrong for the mode it is really in.
Psychology
Narrative fallacy
The habit of linking separate past facts into one explanation and trusting it more than the facts support, named by Nassim Nicholas Taleb in 2007.
Business
Pain of Paying
The pain of paying is the unpleasant feeling of handing over money, which varies with how and when the payment is made.
Design
Universal Design
Designing products, buildings and services so the widest range of people can use them as they are, without special versions.
Design
Accessibility evaluation
Accessibility evaluation checks a product against an accessibility standard to find barriers that stop people with disabilities from using it.
Marketing
Affect Heuristic
A mental shortcut in which a quick good or bad feeling about something is used as information when judging its risk, benefit or value.
Research
Analytical Honesty
Reporting every analysis choice, result and limit of a study as it happened, including results that go against the hypothesis.
Psychology
Anthropomorphism
The tendency to attribute human traits, such as intentions, feelings and thoughts, to things that are not human, including animals, machines and storms.
Psychology
Bandwagon Effect
The tendency to favour a belief, product or choice more because many other people already favour it.
Business
Bundling and Unbundling
The choice between selling things together as one package and selling each part on its own, and how to tell which one fits.
Design
Color Theory
The set of principles describing how colors mix, change each other side by side, combine into schemes and carry meaning.
Marketing
Humanization
Giving a brand human qualities, such as a conversational voice and named people, so customers deal with a person, not an institution.
Marketing
Segmentation
Dividing a market into groups of buyers with different wants, so each group can get a product, price or message suited to it.
Design
Tesler's Law
Tesler's Law states that every application has an irreducible amount of complexity, so design can only choose whether the user, the application developer, or the platform developer deals with it.
AI & Engineering
Agent Loop
The cycle in which an AI agent decides, runs a tool, reads the result and decides again, until the task is done or a limit is reached.
AI & Engineering
Few-Shot Learning
Few-shot learning is giving a model a handful of example input-output pairs inside the prompt itself, so it infers the task and applies it to a new input without any retraining.
Research
Field Testing
Testing a nearly finished product by letting real people use it in their own settings, to find what a lab cannot show.
Design
Figure-Ground
Figure-ground is the Gestalt principle that a scene splits into a figure the eye focuses on and a ground it sits against, decided by cues like contrast, size, and shape.
Psychology
Fogg Behavior Model
The Fogg Behavior Model says a behavior happens only when motivation, ability and a prompt are all present at the same moment.
Product
Forcing Function
A forcing function is a deadline or commitment a product team sets on purpose so a decision gets made instead of deferred.
Psychology
Gestalt Psychology
A school of psychology holding that people perceive organized wholes before parts, which produced the grouping laws designers use.
Marketing
Hook
The opening line, image, or moment of a piece of content that gives a person a reason to keep reading or watching.
AI & Engineering
Loss Function
A loss function is the single number a training algorithm tries to minimize, measuring exactly how wrong a model's prediction is for one example.
Marketing
Price Anchoring
A pricing tactic that shows a reference price first so the price the seller wants judged looks lower beside it and earns a higher willingness to pay.
Marketing
Priming
A cognitive effect where exposure to one stimulus changes how fast or how a person responds to a later, related stimulus, usually without conscious awareness.
AI & Engineering
Prompt Injection Attacks
Prompt injection is an attack that hides instructions inside text an AI system reads, causing it to follow the attacker's commands instead of its own.
Marketing
Search Engine Optimisation (SEO)
SEO is the work of making a website easy for search engines to find, understand and rank, so its pages appear in unpaid search results.
Marketing
Search Intent
Search intent is the goal behind a search query, such as learning, reaching a known site, comparing options or buying, which decides what kind of page satisfies the searcher.
Marketing
Tone of Voice
Tone of voice is how a brand or writer sounds in words, shown through formality, humor, respect and enthusiasm.
Psychology
Action Bias
The tendency to choose doing something over doing nothing, even when waiting would work as well or better.
Design
Banner blindness
Banner blindness is the habit of skipping page elements that look like ads or sit where ads usually go, even when they hold what a person needs.
Design
Law of Common Region
The Law of Common Region is the Gestalt principle that elements inside the same enclosed area are perceived as a group, even against spacing or similarity.
Design
Legibility vs Readability
Legibility is how easily a reader tells characters apart; readability is how comfortably a reader follows whole lines, paragraphs and sentences.
Business
Recall
The share of actual positive cases that a classifier or search system finds: true positives divided by all real positives, so a miss lowers it and a false alarm does not.
Design
Typography Scale
A typography scale is a fixed set of font sizes, usually built by multiplying a base body size by one ratio, that a design uses for all its text.
Design
Visual Anchors
A visual anchor is the element on a page or screen that people look at first and use as the starting point for reading the rest.
Design
Visual Weight
Visual weight is how strongly an element attracts the eye compared with its surroundings, shaped by size, colour, contrast, position and space.
AI & Engineering
Activation Function
An activation function is the rule a single neuron in a neural network applies to its combined input before passing a signal onward, turning a plain weighted sum into a nonlinear value so the network can learn curves rather than only straight lines.
Product
Compromise Effect
People tend to choose the middle option in a set, so adding a more extreme option can raise the share of the option that becomes the middle one.
Design
Continuity
Continuity is the Gestalt principle that viewers group elements lying along a smooth line or curve into one object.
Marketing
Decoy Effect
A third option that is worse than one of two choices on every measure makes people pick that better choice more often.
Design
F-Pattern
The F-pattern is the tendency of eyes to scan text-heavy web pages with little formatting in an F shape: across the top, across a shorter line lower down, then down the left edge.
Psychology
Gamification
Gamification is the use of game design elements, such as points, streaks and badges, in products that are not games, to change what people do.
Psychology
Hindsight Bias
The tendency to see a past outcome as having been predictable, once you already know that it happened.
Psychology
Inattentional Blindness
Failing to see a fully visible object because attention was committed to something else, even while looking directly at it.
Product
Internal Trigger
A feeling or thought, such as boredom or uncertainty, that brings a product to mind and prompts its use without any outside reminder.
Design
Meaningful Friction
A delay, effort or extra step added on purpose before an action that matters, so the person decides with attention.
Product
Parkinson’s Law
Parkinson's Law says work expands to fill the time allotted for it, a satirical claim from 1955, not a tested scientific finding.
AI & Engineering
Postel's Law
A design rule for software that exchanges messages: send strictly by the specification, and accept small deviations when their meaning is clear.
Psychology
Preattentive Attributes
Preattentive attributes are visual properties, such as colour, size and motion, that the eye picks out across a whole scene in one glance.
AI & Engineering
AI Alignment
The work of making AI systems pursue the goals people actually intend, not only the literal objective they were trained to maximise.
Marketing
Barriers to Purchase
Any reason that stops an interested buyer from completing a purchase, such as unexpected cost, perceived risk, missing information, distrust or effort.
Psychology
Choice Closure
The sense that a decision is final, which stops a person from going back over it and comparing it with the options given up.
Product
Double Diamond
A design process model drawn as two diamonds: explore and define the right problem first, then explore and deliver the right solution.
Design
Gulf of Execution
The distance between what a person wants to do and the actions a product lets them find and carry out.
Psychology
Hedonic Treadmill
The hedonic treadmill is the theory that people return to a fairly stable level of happiness after good or bad life events, because they adapt to new circumstances and compare them with a new normal.
Psychology
IKEA Effect
The rise in how much people value something they built themselves, which appears only when the building was finished successfully.
Design
Libertarian Paternalism
Libertarian paternalism is the idea that organizations may design choices to guide people toward their own good while leaving them free to opt out.
Design
Metaphorical Mapping
The set of pairs that carries what people know about a familiar domain, like a wastebasket, onto an unfamiliar one, like deleting files on a computer.
Design
Mind mapping
Mind mapping is a way to organise ideas by placing one topic in the centre of a page and branching related ideas outward from it.
Product
Next Action
The one physical, visible step you can take next on a stalled piece of work, written down so that starting needs no more thinking.
AI & Engineering
Online Learning
In machine learning, updating a model's parameters incrementally on each new example as it streams in, rather than training once on a fixed batch, so the model keeps adapting to new data without being retrained from scratch.
Design
Peak-End Rule
The peak-end rule says people judge a past experience mostly by its most intense moment and its final moment, not by its total or average.
Psychology
Self-Efficacy
Your belief that you can do one particular task, and why that belief decides how hard you try and how long you keep going.
AI & Engineering
Self-Supervised Learning
Training a model on unlabeled data by hiding part of each example and having the model predict the hidden part from the rest.
AI & Engineering
Backpropagation
The method a neural network uses to find how much each weight added to its error, by working backward from the output through the layers.
Marketing
Brand Story
The account a company tells about why it exists, what it believes and what it did about it, told from the customer's side.
Design
Change Blindness
The failure to notice a large, visible change to a scene when it happens during a brief interruption in viewing, such as a blink, an eye movement, or a video cut.
AI & Engineering
Data Leakage
In machine learning, information reaching a model during training that it would not have at prediction time, producing test scores that do not survive deployment.
Marketing
Game Theory
How to choose well when your best move depends on what someone else chooses, with real cases from pricing, auctions and platforms.
Psychology
Hawthorne Effect
The tendency for people to change their behaviour because they know they are being observed or studied, which can distort research results.
Psychology
Hyperbolic Discounting
Waiting costs the most over the first short delays, so people drop a plan to wait once the reward is near.
Product
Kano model
A method that ranks product features by how customers react when a feature is present and when it is missing.
Psychology
Law of Prägnanz
The Gestalt principle that people see the simplest, most regular and most stable form that a scene allows.
Product
Participatory design
A way of designing in which the people who will use a product or system share in the design decisions, working with designers on mock-ups and prototypes.
Business
Poka-Yoke
Shigeo Shingo's mistake-proofing from the Toyota Production System: a device or process step that prevents a human error, or flags it at once, before it becomes a defect.
Psychology
Affordance Blindness
Failing to notice an action that works, because nothing visible shows that it is there.
Psychology
Closure
Closure is the Gestalt principle that people perceive an incomplete shape as a complete one, so small gaps in an outline do not break recognition.
Product
Empathy maps
An empathy map is a one-page diagram that organises what a team knows about a user into what they say, think, do and feel.
Marketing
Exclusivity
A strategy that restricts who may buy or join a product, so that access itself raises its perceived value and status.
Business
F1 Score
The harmonic mean of precision and recall, a single score from 0 to 1 that is high only when a classifier finds most positives and few of its flags are wrong.
Design
Information Scent
Information scent is a person's estimate of how likely a link or label is to lead to what they are looking for, made before they click.
Product
Mental model diagrams
A research chart that groups how people think about a purpose into towers, with an organization's support lined up beneath to expose gaps.
Psychology
Miller's Law
George Miller's 1956 finding that immediate memory holds about seven chunks of information, not seven separate items.
Marketing
Reference Point
The level a person compares an outcome with, which decides whether that outcome feels like a gain or a loss.
Research
Sampling
Sampling is choosing a subset of a population to study so the results can describe the whole group, using either random selection or convenience and judgment.
Research
Abductive Reasoning
Choosing the explanation that best accounts for a surprising observation, as a plausible working answer that must still be tested against rivals.
Design
Atomic Design
A method for building design systems from five levels of interface parts: atoms, molecules, organisms, templates and pages.
Business
AUC
The area under a classifier's ROC curve: the probability that the model scores a random positive example higher than a random negative one, across every possible cutoff.

Every term worth knowing — a concept library for designers, PMs, engineers, founders, and tech leaders. Page 2 of 11.