Meteors are mostly made up of rock and iron, and they come from either asteroids or comets. When fragments of an asteroid or a comet break off, they are called meteoroids while they travel through space. When a meteoroid enters the Earth's atmosphere, it becomes a meteor.
If a meteor is large enough to withstand the intense heat of entry into the atmosphere, and it lands on the Earth's surface, it is called a meteorite. Most meteor showers occur as the Earth passes through the debris left over by a passing comet. The Hoba meteorite in southwest Africa is one of the biggest meteorites; it weighs about 119,000 pounds.