JavaScript is a high-level programming language that brings interactivity to web pages. It runs directly in the browser and can also be used on the server through environments like Node.js. Along with HTML and CSS, JavaScript forms one of the core technologies of the modern web. It supports multiple programming styles, including object-oriented, functional, and event-driven development. Modern versions of JavaScript (ES6 and later) introduce useful features such as modules, arrow functions, and async/await, making it easier to build scalable and maintainable applications.