A lobby is a large waiting room or reception area. If you're waiting for an appointment in a lobby, maybe you'll get lucky and find a good magazine or even a peppermint candy.
You'll find a lot of people hanging around in a lobby — which is basically what it’s there for. A lobby is where you meet your friend at the hotel or catch the elevator for your interview. The idea of the "political lobby group" came from the large entrance halls of the legislature, where people hung around trying to influence the lawmakers. So the next time your class tries to lobby your teacher for extra credit, he can thank the halls of Congress.