CURL is a command line tool for transferring data with URL syntax, supporting DICT, FILE, FTP, FTPS, GOPHER, HTTP, HTTPS, IMAP, IMAPS, LDAP, LDAPS, POP3, POP3S, RTMP, RTSP, SCP, SFTP, SMTP, SMTPS, TELNET and TFTP. curl supports SSL certificates, HTTP POST, HTTP PUT, FTP uploading, HTTP form based upload, proxies, cookies, user+password authentication (Basic, Digest, NTLM, Negotiate, kerberos...), file transfer resume, proxy tunneling and a busload of other useful tricks.

It's free and open software that compiles and runs under a wide variety of operating systems. Curl exists thanks to efforts from many contributors. The most recent stable version of curl is version 7.23.1, released on 17th of November 2011. Currently, 3 of the listed archives are of the latest version.

You might have faced the problem "CURL library is unavailable on this server". I've  faced this problem many times working on video upload in joomla CMS.

To enable CURL library, need to modify the php.ini files in your xampp folder.

1) Locate the following files:
C:Program Filesxamppapacheinphp.ini
C:Program Filesxamppphpphp.ini
C:Program Filesxamppphpphp4php.ini

2) Uncomment the following line on your php.ini file by removing the semicolon.

 ;extension=php_curl.dll change to extension=php_curl.dll

3) Restart your apache server.

4) Check your phpinfo if curl was properly enabled.