What does this mean on Twitter?

[Taylor]

I just got a Twitter account and i see tons of people using #janedoe

What does it mean exactly? I know tagging people is '@' but what is the '#'?

[Bobby]

i think it's referring to a topic

[hummingbird]

it's a topic that may be trending, or that someone wants to trend. like if you click on the #..... you'll see people that have tweeted using that same thing. e.g "just tripped over my own feet in front of everyone #failwhale " so basically just a topic of the tweet, it can be anything really. like i saw one #thingsihaveincommonwithjesus or #iTunesfestival, or if you're talking about eclipse you might put #Eclipse after it so people that want to see tweets about that movie will see yours.