An asteroid is a large rock that moves around the sun. Some of these are considered large and some are small, but they are made of dust particles in space. A meteor is similar to an asteroid because they are both rocks from space. Meteoroids come from asteroids. While the asteroids are moving around in space, they may hit something and break apart. These smaller pieces are called meteoroids.
When the meteoroid slams into the earth, it becomes known as a meteorite. So, the location of the space rock is a key factor in determining the name of it. Those that are large and in space are the asteroids and those that have hit the ground are known as the meteorites.