What does # mean in the internet?

[mOunstrO]

I keep seeing it everywhere. Ex. #Team Jacob. O_o

[Megan]

It's a hashtag and it is used on Twitter to like call someone out. Example #HardRockRocks its a cafe so like your speaking to that user and it can also mean number

[Dean]

Hashtags became popular because of a pretty boring site called 'Twitter'.

The human race, condensing the random crap we think, into 140 characters.

I honestly wonder how much pointless sh!t is on the net.

[Jonathan]

its either a hashtag from twitter, or a channel on an IRC network.