#! In a URL, what does it mean ?

Question

Possible Duplicate:
What's the shebang (#!) in Facebook and new Twitter URLs for?

#! What does it mean in a URL ? I found it in facebook & twitter url !

http://www.facebook.com/#!/
http://www.facebook.com/#!/?sk=messages
http://www.facebook.com/#!/?sk=ff&ap=1

http://twitter.com/#!/messages
http://twitter.com/#!/BillGates

Answer 1

This is called the shebang URL hash, used to hint to search engines that this site is using Ajax to display another page.

Answer 2

It is meant for AJAX and Google indexing.