what is curl in http code example

Example 1: curl get example

curl -i -H "Accept: application/json" -H "Content-Type: application/json" -X GET http://hostname/resource

Example 2: what is curl in api

curl is a command line client to send request and
get respond from command line, so it's basically 
it's just way to send a request and response. Where you
send it we call it client. But with postman we can do more
than just sending request end respond.
This tool is preferred for automation, 
since it is designed to work without user interaction.
curl can transfer multiple file at once.