What is this i see on tv? "#insertshowhere"? what's it for?

[laraliu]

i've been watching tv and ive noticed stuff pop into the bottom of the screen, just over the channel logo, and stay there the whole show.
#dancemomsmaimi
#glee
#dwts (dancing with the stars i was watching)
i saw it on a commercial too, it was like #product
i've also seen it on youtube, the channel FineBros did a post the other day and they told viewers to comments #greatbeards or something
what's it for?

[♥Rachel♥]

It's a hashtag for twitter. Its so you can tweet along with others who are watching the show so you use that hastag
So if you were watching like Dancing with the Stars you would Say like Maybe I love Katherine and Mark they were amazing #DWTS
It's just a thing to tweet along with the show and other people who are watching it