JavaScript is a high-level, interpreted programming language primarily used for creating dynamic and interactive content on websites. It enables developers to implement features such as form validation, interactive maps, and real-time updates without requiring page reloads. As a client-side language, JavaScript runs directly in the user's browser, but it can also be used on the server side through environments like Node.js. With its ability to manipulate HTML and CSS, JavaScript plays a crucial role in modern web development, allowing developers to create responsive, engaging user experiences.