JavaScript is a versatile, high-level programming language used to make websites interactive and dynamic. It runs directly in the browser and allows developers to create animations, handle events, and update content without reloading the page. JavaScript is a core part of web development, alongside HTML and CSS, and it powers modern web frameworks and libraries like React, Angular, and Vue.js. With advancements like Node.js, JavaScript is now used for both client-side and server-side programming.