React is a popular JavaScript library for building user interfaces, particularly single-page applications. It's used for handling the view layer for web and mobile apps.

Some key features of React include: Virtual DOM for better performance, JSX for easier component writing, component-based architecture, unidirectional data flow, and strong community support.

JSX is a syntax extension for JavaScript. It was written to be used with React. JSX code looks similar to HTML, making it easier to write and understand the structure of React components.

The Virtual DOM is a programming concept where an ideal, or 'virtual', representation of a UI is kept in memory and synced with the 'real' DOM. This process is called reconciliation, and it's what makes React fast.

React Hooks are functions that let you 'hook into' React state and lifecycle features from function components. They were added in React 16.8 and include useState, useEffect, useContext, and more.