Meteor is the name given to an object as it falls through the Earth's atmosphere. The same object is called a meteoroid when it's outside the atmosphere and a meteorite when it's found intact on the Earth.
Meteors usually become visible when they reach an altitude of 60 miles, at which point they're seen as fiery streaks due to compression. When meteors travel at extremely high speeds it causes the air ahead of them to compress. The heat of this compression is transferred to the meteor, which starts to glow.
Countless meteors enter the Earth's atmosphere every year, but most of them weigh less than an ounce. Even bright meteors usually weigh less than 5 pounds and don't typically survive to reach the Earth's surface.
Meteor showers occur when the earth passes through the path of a cluster of meteoroids. These meteors are sometimes the remnants of comets. Famous meteor showers happen 18 times a year, and they tend to come from the direction of a constellation, after which they've received their names. The Leonids come from the constellation Leo, the Orionids come from Orion and the Perseids come from the constellation Perseus. Meteor showers typically last for several days.