GlossaryUpdated
Product design and development glossary
Plain definitions of the terms that come up when you plan, design, and build a web or mobile product. Each entry says what the term means, when it matters, what it costs, and the mistakes to avoid.
Building software
- Application programming interface (API)An API (application programming interface) is a defined way for one piece of software to ask another for data or actions, such as an app asking its server for a user's orders or asking a payment provider to charge a card.
- BackendThe backend is the part of a product that runs on servers instead of on the user's device. It stores data, checks who is allowed to do what, runs business rules, and connects to other services, and apps reach it through an API.
- Core Web VitalsCore Web Vitals are three Google metrics for real-world page experience: Largest Contentful Paint (loading), Interaction to Next Paint (responsiveness), and Cumulative Layout Shift (visual stability), measured from actual visits.
- Custom mobile appA custom mobile app is an iOS or Android app designed and built for one product and installed from the App Store or Google Play. It earns its place when the job depends on the phone itself, such as the camera, location, notifications, or working offline.
- Custom web applicationA custom web application is software built for one business that people sign in to and use in a browser, such as a dashboard, a customer portal, an internal tool, or a SaaS product. Its job is to let users do work with their own data.
- Custom websiteA custom website is a site designed and built for one business, rather than assembled from a template or a site builder's stock layouts. Its design, page structure, and content editing all follow how that business sells and publishes.
- FlutterFlutter is an open-source framework from Google for building apps for iOS, Android, web, and desktop from one codebase, written in the Dart language, that draws its own interface instead of using each platform's built-in components.
- Headless CMSA headless CMS is a content management system that stores and edits content in one place and delivers it through an API to any front end, such as a website, a mobile app, or an in-store screen. It does not build the pages itself.
- Native vs cross-platform appsNative apps are built separately for each platform with Apple's and Google's own tools, such as Swift for iOS and Kotlin for Android. Cross-platform apps share one codebase across both, using frameworks like React Native or Flutter.
- Next.jsNext.js is an open-source React framework, created and maintained by Vercel, for building websites and web applications. It adds routing, server rendering, and data loading to React, so pages can be fast, readable by search engines, and full-featured.
- No-code vs custom codeNo-code tools let people build websites, apps, and automations by configuring visual building blocks instead of writing code. Custom code is software written by developers, which takes longer to build but can do whatever the product needs and runs wherever you choose.
- Progressive web app (PWA)A progressive web app (PWA) is a website built to behave like an installed app: it can be added to the home screen, open in its own window, work offline, and on supported platforms send push notifications, all from one web codebase.
- QA testingQA (quality assurance) testing is the work of checking that software does what it should before people rely on it, through automated tests that run on every change and manual testing of real flows on real devices.
- React NativeReact Native is an open-source framework from Meta for building iOS and Android apps from one codebase in JavaScript or TypeScript, using React, while showing each platform's own native interface components.
- Software as a service (SaaS)Software as a service (SaaS) is software that people use through a browser or app while the provider hosts and maintains it, usually paid for by subscription instead of a one-time license.
- Tech stackA tech stack is the set of languages, frameworks, databases, hosting, and third-party services a product is built and run with, from the screens people use down to the servers that store their data.
Design
- Design handoffA design handoff is the step where designers pass finished designs to developers to build, along with the specs, assets, states, and notes needed to turn screens into working software.
- Design systemA design system is a shared set of design tokens, components, patterns, and usage guidelines, usually mirrored in code, that a team uses to build a product that stays consistent and is faster to extend.
- Information architecture (IA)Information architecture (IA) is how the content and features of a website or app are organized, grouped, and labeled, so that people can find what they need and understand where they are.
- Landing pageA landing page is a single web page built for one purpose, such as getting sign-ups, bookings, or purchases, usually for visitors arriving from an ad, an email, a launch post, or a search.
- Product designProduct design is the work of deciding what a digital product should do, how it works, and how it looks, from the first problem to the shipped screens, with each choice tied to a business goal.
- PrototypeA prototype is a working model of a product, built to test an idea with real people before you pay to build it properly. It can be drawn on paper, clicked through in a design tool, or written as a small piece of real code.
- UI designUI design (user interface design) is the design of the visual and interactive layer of a product: layout, typography, color, components, and how each control looks and responds in every state.
- User flowA user flow is the path a person takes through a product to finish one task, from the point where they arrive to the point where the task is done, including the screens, choices, and outcomes along the way.
- UX auditA UX audit is a structured review of a live product to find where people struggle, using usability principles, analytics, and accessibility checks, and ending in a prioritized list of problems and fixes.
- UX designUX design (user experience design) is the work of shaping how a product works for the person using it: the steps they take, how information is organized, and how the product responds, checked with real users through research and testing.
- Web accessibility (WCAG)Web accessibility means building websites and apps that people with disabilities can use, including people who rely on screen readers, keyboards, captions, or zoom. WCAG is the W3C standard most laws and audits use to measure it.
- WireframeA wireframe is a low-fidelity layout of a screen that shows its structure and content priority (what goes where and what matters most) without visual style such as color, imagery, or final typography.
Product
- A/B testingA/B testing is comparing two versions of a page, screen, or feature by showing each to a random half of users at the same time, then measuring which one performs better on a goal chosen in advance.
- Minimum viable product (MVP)A minimum viable product (MVP) is the smallest version of a product that real users can use to do one real job, built to learn whether the idea works before you spend more on it.
- Product analyticsProduct analytics is measuring what people do inside a product by recording events, such as signed up, created a project, or invited a teammate, so a team can see which steps work, where people drop off, and who comes back.
- Product discoveryProduct discovery is the work of deciding what to build and for whom before committing to a build. It tests the riskiest assumptions with real people through interviews, prototypes, and prioritization, so the build starts from evidence.
- Product roadmapA product roadmap is a short, shared plan of what a product team intends to work on and why, usually grouped by time horizon or goal, that helps everyone agree on priorities without promising exact features on exact dates.
- Product-market fitProduct-market fit is when a product meets a real need for a specific group of customers well enough that they keep using it, pay for it, and tell others, so growth starts to come from demand rather than pushing.
- Usability testingUsability testing is watching real people try to complete set tasks with a design or product, so you can see where they get confused, slow down, or give up. The product is being tested, never the person.
- User activationUser activation is the moment a new user first gets real value from a product, defined as a specific action such as sending a first invoice. The activation rate is the share of new sign-ups who take that action.
- User onboardingUser onboarding is everything a product does to get a new user from signing up to getting real value for the first time, including the sign-up itself, any setup, the first screens they see, and the messages that follow.
- User researchUser research is the practice of learning how real people behave, what they need, and where they struggle, through methods such as interviews, observation, surveys, and testing, so product decisions rest on evidence instead of guesses.
- User retentionUser retention is the share of people who keep using a product over time after they first start. It is usually measured by cohort, comparing how many users from each starting week or month are still active later.
AI
- AI-assisted designAI-assisted design is product design where designers use AI tools to generate layouts, copy drafts, images, and research summaries faster, while people still decide what the product should do, how it should feel, and what ships.
- AI-assisted developmentAI-assisted development is writing software with AI coding tools that suggest, generate, and edit code, while engineers decide the architecture, review every change, and stay responsible for how the software behaves.
- Answer engine optimization (AEO)Answer engine optimization (AEO) is making a website easy for AI assistants and AI search features, such as ChatGPT, Perplexity, and Google's AI Overviews, to find, understand, and cite when they answer people's questions.
- llms.txtllms.txt is a proposed standard for a Markdown file at the root of a website, at /llms.txt, that gives large language models a short summary of the site and links to the pages that matter most, in a form they can read easily.
- Vibe codingVibe coding is building software by describing what you want to an AI tool and accepting the code it writes without reading it closely, judging the result only by whether it seems to work. Andrej Karpathy coined the term in February 2025.
Working with a studio
- Fixed-price developmentFixed-price development is a way of buying software where the studio agrees to deliver a written scope for one total price, set before work starts. The usual alternative, time and materials, bills for the hours actually worked.
- Product development retainerA product development retainer is a monthly agreement where a studio or agency reserves design and development capacity for one client's product, for a set fee, so improvements ship continuously without scoping each change as a new project.
- Scope of workA scope of work is the written document that says what a studio or contractor will deliver, by when, for how much, and what is not included. Both sides use it to decide whether the work is done.
- Technical debtTechnical debt is the future cost of shortcuts and outdated decisions in a codebase. Like a loan, it lets you move faster now, and you pay interest later as every change takes longer until the debt is paid down.
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