Why do people put a "#" in front of words on facebook and whatnot?

[Emma Tucker]

So I was looking at Facebook stuff and some people post stuff like #faded and what not... I don't get it....

[Brooke]

Some people use Twitter hashtags (An item on Twitter used to talk about something) on Facebook, which to me doesn't make any sense, & gets #annoying.

[Kelly]

People forget that Facebook isn't Twitter. It's called a hash tag.

[abraXus]

those are hash tags that are used for using trends on twitter

the reason the sometimes show up on facebook is because people are updating their twitter and have that linked to their facebook, so the # sign shows up on facebook too