A gym is short for gymnasium, a room or building designed for physical exercise and sports. At school, gym class happens in the gym, where you might play basketball, climb ropes, or learn new games. Many adults belong to a gym where they lift weights, run on treadmills, or take exercise classes.

Greek athletes trained in gymnasiums for competitions like the Olympic Games. These original gymnasiums were also places where people discussed philosophy and ideas, combining physical and mental development.

Today, gyms come in many forms. A school gym usually has a basketball court and equipment for different activities. A fitness gym might have rows of exercise machines and free weights. Some gyms specialize in specific activities like gymnastics, rock climbing, or martial arts.

People also use “gym” to refer to the class itself, as in “I have gym after lunch.” And when someone says they're “going to the gym,” they mean they're going to work out and exercise, whether that's lifting weights, swimming, or playing sports.