A gymnasium is a large indoor room or building designed for physical exercise and sports. The word comes from ancient Greece, where young men trained and competed in athletic events. Greek gymnasiums were outdoor spaces where athletes practiced wrestling, running, and throwing the discus.

Today's gymnasiums look quite different. Most schools have a gym where students play basketball, volleyball, or dodgeball during physical education class. The floor is usually made of polished wood, and the walls might have climbing ropes, basketball hoops, or folded bleachers. Community centers and health clubs also have gymnasiums for sports leagues and fitness activities.

Outside the United States, particularly in Europe, a gymnasium can mean something completely different: a type of academic secondary school that prepares students for university. A German student attending a Gymnasium isn't necessarily playing sports; they're studying subjects like mathematics, languages, and science in a rigorous academic program.

The informal shortening gym usually refers to either a school gymnasium or a fitness center where people exercise with weights and machines. When someone says “I'm going to the gym,” they typically mean a place to work out, not a school gymnasium.