What does it mean when someone writes # then a word- on facebook?

[Tiffany]

I keep seeing people use this on facebook. They write a status and at the end of their status do the number sign (#) then a word?? what does this mean

[ljkoij]

It’s what’s called a “hash-tag,” and it’s used to “tag” certain topics on the popular social networking website Twitter.

[Davonta]

Ive been seeing that alot on facebook lately too, On Twitter it's used for trending topics so people on facebook are doing the same thing.

[love116]

It pretty much gives emphasis to the word right after the # sign...

Like: 'The movie, the Hangover, was #hilarious'.....