Why do people use "#" on Twitter a lot?

[William]

[Andy]

Its called a hash tag and used alot to say something

[Danielle:)]

Is called a hashtag, you put for example #Fml and if you click it you can see every tweet someone put with the same hashtag.

[jaylaynaykaybetty]

It's called a hash tag.A hash tag is simply a way for people to search for tweets that have a common topic. For example, if you search on #LOST (or #Lost or #lost, because it's not case-sensitive), you'll get a list of tweets related to the TV show. What you won't get are tweets that say "I lost my wallet yesterday" because "lost" isn't preceded by the hash tag.