A heater is a device that produces warmth to make a space or object more comfortable. When winter arrives and your house gets cold, you turn on the heater to warm the air inside. Schools have heaters to keep classrooms comfortable during freezing weather. Cars have heaters that blow warm air to defrost windows and keep passengers cozy.

Heaters work in different ways. Some burn fuel like natural gas or oil, while others use electricity to generate heat. A space heater warms up a single room, while a furnace heats an entire building. Water heaters heat the water that comes out of your shower and kitchen faucet.

In baseball slang, a heater means a fastball, a pitch thrown with maximum speed and power. When a pitcher throws a heater, the ball blazes toward home plate at speeds that can exceed 90 miles per hour. You might hear an announcer say, “He's really bringing the heat today!” when a pitcher is throwing especially hard.

The word suggests something that brings warmth or intensity, whether it's making your bedroom comfortable on a snowy morning or delivering a baseball with serious speed.