What's the shebang/hashbang (#!) in Facebook and new Twitter URLs for? -

i've noticed long, convoluted facebook urls we're used this:

http://www.facebook.com/example.profile#!/pages/another-page/123456789012345

as far can recall, earlier year normal url-fragment-like string (starting #), without exclamation mark. it's shebang or hashbang (#!), i've seen in shell scripts , perl scripts.

the new twitter urls feature #! symbols. twitter profile url, example, looks this:

http://twitter.com/#!/boltclock

does #! play special role in urls, ajax framework or since new facebook , twitter interfaces largely ajaxified? using in urls benefit web application in way?

this technique now deprecated.

this used to tell google how index page.

https://developers.google.com/webmasters/ajax-crawling/

this technique has been supplanted ability use javascript history api introduced alongside html5. url www.example.com/ajax.html#!key=value, google check url www.example.com/ajax.html?_escaped_fragment_=key=value fetch non-ajax version of contents.