A syntax extension for JavaScript that looks like HTML and is used to describe UI in React. JSX is compiled to React.createElement() calls. It supports JavaScript expressions inside curly braces {}.

Short for properties — the mechanism for passing data from parent to child components in React. Props are read-only and flow downward (one-way data flow). Destructure props in function parameters for clean code.

Data that a component manages internally and can change over time. When state updates, React re-renders the component. Use useState for simple state and useReducer for complex state logic.