What is the function of the -d option in Curl?

The -d option in Curl is specifically used to pass data to the server in the body of a request, typically for POST requests. When you use this option, Curl sends the specified data in the request, allowing you to submit forms or send other data payloads to a web server.

For example, if you are interacting with a REST API and need to send JSON data as part of a POST request, using the -d option followed by the data will ensure that it is included in the request body. This feature is crucial for many web applications that require client data to be sent for processing or storage.

Other options may relate to various functionalities such as debugging or header definition, but they serve different purposes and are not associated with data transmission in the request body.