Asteroids are relatively small, rocky objects that orbit the sun. Astronomers occasionally call them “minor planets,” or sometimes “planetoids.” They generally move in eccentric trajectories between Mars and Jupiter in an area known as the asteroid belt, located between 2.1 and 3.3 A.U. from the Sun. There are not many that are larger than 300 km in diameter, and most are as small as a tenth of a kilometer across. The largest known asteroid, Ceres, and has 1/10/000 the mass of Earth measuring only 940 km across.
According to NASA, “An asteroid is a small rocky object that orbits the Sun. Asteroids are smaller than a planet, but they are larger than the pebble-size objects we call meteoroids. A meteor is what happens when a meteoroid – a small piece of an asteroid or comet – burns up upon entering Earth’s atmosphere, creating a streak of light in the sky.”