Why PHP?
To keep it short. It's free, open source, cross-platform, stable, fast and easy to learn.

What is PHP?
PHP stands for Hypertext Preprocessor, well thats whats its named now. First it had the name Personal Home Page Tools. PHP is a server-side HTML embedded scripting language. PHP is sometimes called "the open source ASP" beacuse its functionality is so similiar to the MS product thing.

License
http://www.php.net/license.html
http://www.troll.no/qpl/annotated.html


Want to learn PHP?
Check out www.php.net or buy a book at www.amazon.com

regards
mits