What is React Hook?

React Hooks are functions that let you “hook into” React state and lifecycle features from function components. They allow you to use state and other React features without writing a class. Commonly used hooks include `useState` for managing local component state, `useEffect` for handling side effects (like data fetching or DOM manipulation), `useContext` for accessing context values, `useRef` for creating mutable values that persist across renders, and `useMemo` and `useCallback` for performance optimization by memoizing expensive calculations and function instances, respectively. Custom hooks can also be created to encapsulate reusable stateful logic.