PHP stands for "Hypertext Preprocessor" [recursive acronym], a very popular open source server side scripting language allows users to develop rich, effective and scallable web portals and web applications. It was created by "Rasmus Lerdorf". It can be run under IIS, apache and other popular web servers.

Sites developed using PHP:

1. feedburner
2. istockphoto
3. yousendit
4. meebo
5. techcrunch