React (also known as React.js or ReactJS) is a free and open-source front-end JavaScript library for building user interfaces based on UI components. React can be used as a base in the development of single-page, mobile, or server-rendered applications with frameworks like Next.js. However, React is only concerned with state management and rendering that state to the DOM, so creating React applications usually requires the use of additional libraries for routing, as well as certain client-side functionality.
React is commonly used for Single Page Applications (SPAs) and Client-Side Rendered (CSR) applications. SPAs involve a browser receiving a single static HTML document and a JS file that renders everything else. Developers can also integrate React with other technologies to create full-stack applications, like MongoDB, Express, Node.js, and React (MERN) Stack.
Compared to other front-end frameworks like Angular and Vue, React offers some unique features and advantages. For example, React uses JSX syntax, which allows developers to write HTML-like code within JavaScript, making it easier to create and maintain UI components.