Not quite the right way of thinking about it.

curl is a program that can be used from a terminal.

Servers are often interacted with via URLs.

curl is just one of many tools for interacting with them.

If you have access to a terminal with curl installed I would suggest running man curl and having a read of the output.

Alternatively it can be read here:

https://www.man7.org/linux/man-pages/man1/curl.1.html