JavaScript is a high-level, dynamic programming language commonly used to create interactive and dynamic content on websites. It enables developers to implement complex features such as form validations, animations, and asynchronous requests (AJAX) to update web content without reloading the page. JavaScript runs in the browser and can interact with HTML and CSS to modify the user interface, enhance user experience, and provide real-time updates. It is supported by all modern web browsers and, with the advent of frameworks and libraries like React, Angular, and Vue.js, has become a crucial tool in modern web development. Additionally, JavaScript can be used on the server side with environments like Node.js, making it a versatile language for both frontend and backend development.