JavaScript is a high-level, dynamic programming language commonly used for creating interactive and dynamic features on websites. It runs in web browsers, allowing developers to manipulate web page content, handle user events, validate forms, and perform asynchronous tasks like fetching data without reloading the page. JavaScript is essential for building modern web applications and works seamlessly with HTML and CSS. It supports object-oriented, functional, and imperative programming styles, making it versatile for both front-end and back-end development, especially with frameworks like Node.js.