Its an amalgam of Apache Web Server, Mysql Database Server, and PHP Scripting/Programming Language. Some people would like to include Perl and Python into the mix. Thats fine because they are similar to PHP. However, this website focuses more on PHP.

When you run AMP on a Windows box, it becomes WAMP. MAMP and LAMP on Mac OS and Linux respectively. There are so many websites focusing on AMP resources. I give some basic information on AMP tools but I am sure if you typed AMP on google, you would find so many links to resources.

Apache Friends Xampp
Runs on Linux, Solaris, Mac OSX, and Windows. PHP is 4.x and 5.x and switchable.

MAMP
Runs on Mac OX only.

WAMP
Runs on Windows only and you can switch between PHP4 and 5.

Apache2Triad
Runs on Windows only and features apache 2.2

The Uniform Server
Runs on Windows only.