A gym is a building or room that's meant for playing indoor sports or exercising. You might go to the gym to pump iron, or you might go to the gym to see who else is pumping iron. The word gym is a shortened form of gymnasium, originally a Latin word meaning "school for gymnastics," from the Greek gymnasion, "public place where exercises are practiced." The preferred way to dress at a gym these days is in shorts or sweatpants, but back in Ancient Greece, men commonly exercised naked — hence the root gymnazein, "to train naked."