What is curl? What is the functionality of curl?

What is curl? What is the functionality of curl?
PHP supports libcurl a library created by Daniel Stenberg that allows you to connect and communicate to many different types of servers with many different types of protocols. libcurl currently supports the http https ftp gopher telnet dict file and ldap protocols. libcurl also supports HTTPS certificates HTTP POST HTTP PUT FTP uploading (this can also be done with PHP's ftp extension) HTTP form based upload proxies cookies and user+password authentication.

These functions have been added in PHP 4.0.2.