What Does POTUS Mean On Tweets From Presidential Debate

I'll be the first to admit I don't use my twitter account regularly.  It is quite apparent though that Twitter is becoming the fastest way to comment on events, such as the Presidential debate.  Last night, while watching the debate I was also monitoring tweets from politcal analysts.  A word kept coming up that I actually had to look up:  POTUS.  I honestly hadn't heard what it meant before.  Here's an "ahh duhh..." moment.  It's an acronym for President Of The United States.  See:

Now I feel kinda old, outdated, and silly.  At least now I know.  I'm going to brush up on my twitter, because if Andrea Mitchell can tweet fluently, I better be able to as well.