Curl is a versatile command-line tool for transferring data across various network protocols, widely used for sending HTTP requests, including POST requests, from the command line. It supports multiple protocols such as HTTP, HTTPS, FTP, and IMAP, making it a standard tool in REST API documentation for testing API calls. POST requests, used for sending data to a server, are discreet and allow for more data transmission compared to GET requests. To send a POST request with curl, users must specify the HTTP method with the -X flag, set the Content-Type and Accept headers using the -H flag, and include data in the request body with the -d flag. Curl also facilitates sending different data formats such as JSON, XML, and FormData, and supports basic authentication with the -u flag. The tool is widely available on major operating systems with installation methods varying by platform, and it offers a range of features that can be explored for more advanced data transfer needs.