It's called reputation or "rep", simply put, it's just a little extra thing on the site where if you like a post someone says, you can "rep" them and it'll add to their reputation. The higher your reputation, the more gems you'll have. In turn, you can "derep" someone, and make them lose rep, even get into red rep gems.
Hehe, my friend drew it in the Paint app on my laptop while I was in the shower. I thought it was too cute.
