Definition
A component is a self-contained, reusable piece of a user interface. Instead of building every page from scratch, modern applications are assembled from components — a navigation bar, a search field, a project card, a notification badge. Each component handles its own appearance and behaviour, and can be used in multiple places across the application. If you think of a web page as a wall, components are the individual bricks — each one is built once and placed wherever it is needed.
Why It Matters
Component-based development is how most modern web and mobile applications are built. It matters for business owners because it directly affects how quickly new features can be delivered and how consistent the user experience is. When your application uses well-built components, adding a new page often means arranging existing components rather than building everything from the ground up. It also means that fixing a bug in one component — say, a date picker — fixes it everywhere that component appears, rather than requiring the same fix in ten different places.
Example
A client portal has a “Project Status Card” component that shows a project name, progress bar, and next milestone date. This same component appears on the dashboard, the projects list page, and in weekly email summaries. When the design team decides to add a budget indicator to the card, the developer updates the single component and the change appears everywhere automatically. Without components, they would need to update three separate pages individually — tripling the work and the risk of inconsistency.