An elevator is a machine that carries passengers to higher and lower floors in a tall building. Even though you usually take the stairs to your apartment, when you're exhausted you might decide to take the elevator instead.
Most elevators run on electricity, although in the 19th century the first elevators used steam power to move heavy goods in coal mines. Today, elevators are legally required in tall buildings, so that people who aren't able to climb stairs have access to all floors. In the 1640's, elevator meant "muscles used to raise the body," from the Latin elevator, "one who raises up."