What does this mean in Twitter?

[shining*star]

I know this : ' @ ' is to mention someone for a reply...but what does this means : # ]
like ppl tweets like this (for example): It takes charlie to tango. #modernproverbs
, #raiseyourhandif u r not there ;D,

what does this # sign means ?
but these tags...where do they come from there are no users of that # names ?

[kl]

Click on anything that has the # before it - it's called a hash tag. By clicking on one of those tagged keywords, it will show every other post on Twitter that has the same tag included.

[Saurav]

Its also called hashtags, when you include "#" in your tweet it becomes a keyword, now anyone who searches this word all the tweets will be listed which have that word with a #

Its a way of improved tagging, grouping in twitter

http://twitter.pbworks.com/Hashtags