Why do people put # before their words on Facebook and Twitter?

[Jazzmin N]

[Parvinder]

In many programming languages, # is used for comments.

So, people prefix # where they want to insert a comment.

[CB]

Has to do w/ trending topics.

"You may notice that some topics come with a number sign "#" before the word or phrase. This is called a "hashtag" and was put there specifically to mark it as a topic so that people can follow the conversation in search. Check out this page (http://support.twitter.com/entries/49309) for more information about hashtags."

[Luke Josh]

In twitter, it's called a hashtag, and it's used to categorize your posts. It makes it easier for people to find posts about the things they're looking for.

As for Facebook, the trend has followed over from twitter, but doesn't have as big a meaning as it does on twitter.

[TobiasLuciaStarr]

Put the # before words/phrases makes it a tag, and connects you to others talking about that same thing if you click on it.