Node.js is a JavaScript runtime that can be used for both front-end and back-end development. Node.js is primarily known for its back-end capabilities and is often used to build server-side applications. It allows developers to use JavaScript on the server-side, which can be beneficial for developers who are already familiar with JavaScript and want to use the same language for both front-end and back-end development.

On the back-end, Node.js allows developers to build web servers, APIs and other server-side logic using JavaScript. The package manager for Node.js, npm, has a large number of libraries and modules available, making it easy to build scalable, high-performance back-end applications.

On the front-end, Node.js can also be used to build command line tools, desktop applications, and other types of scripts. It also allows developers to use JavaScript to build automation tasks, such as building and deploying web applications.

In summary, Node.js is a JavaScript runtime that can be used for both front-end and back-end development. However, it is more commonly used for back-end development.