jQuery is a fast, small, and feature-rich JavaScript library. It makes things like HTML document traversal and manipulation, event handling, animation, and Ajax much simpler with an easy-to-use API that works across various browsers.

jQuery simplifies complex JavaScript tasks, allowing you to write less code for the same functionality. It handles cross-browser compatibility issues, making it easier to work on web projects that need to support multiple browsers.

jQuery is less commonly used for new projects as modern JavaScript frameworks (like React, Vue, and Angular) and vanilla JavaScript have become more popular. However, jQuery is still widely used in legacy projects and for smaller tasks due to its simplicity and versatility.