A meteorite is a rock (usually small but sometimes very large) that breaks off of an asteroid, planet, or comet, and falls from space to earth. Due to their immense age and the fact that many of them haven't changed since they formed, meteorites were essential in dating our solar system and continue to provide clues on what the early universe looked like. By recording traces of cosmic rays and solar wind and flares, meteorites allow us to reconstruct the space environment and behavior of our sun.
Meteoroid (in space) → Meteor (in atmosphere) → Meteorite (on earth)