Curl is a command-line tool and library used for transferring data with URLs. It supports various protocols, including HTTP, HTTPS, FTP, and more, allowing users to send and receive data over the internet. Curl is widely used in web development and automation tasks, making it easier to interact with APIs and download files. The tool is known for its versatility and ease of use, enabling users to perform tasks like uploading files, sending form data, and retrieving web pages. With its extensive options and features, Curl is a valuable resource for developers and system administrators alike.