Although the terms asteroid and meteoroid refer to rocky objects in space, they're not interchangeable. Asteroids are the tiny "mini-planets" that orbit the sun in the zone between the terrestrial planets and the gas giants. These generally maintain a fixed orbit, although some cross close to Earth's orbit. Meteoroids are fragments of an asteroid or comet; when they enter the earth's atmosphere, they are called meteors. Those that hit Earth, including asteroid fragments, are called meteorites.
The asteroid belt consists of two belts. The main belt contains large asteroids and thousands of smaller ones. The largest asteroids in the main belt can be observed through a telescope and have been assigned names from Greek mythology, such as Ceres and Hygeia. The secondary, or Trojan, belt of small asteroids orbits closer to Jupiter. Their orbit is dictated by gravitational pulls between Jupiter and the sun.
Asteroids can be classified by size or composition. The main belt contains asteroids of different sizes and shapes, although none has significant mass. Ceres, the largest member of the belt, makes up about 30 percent of its total mass. Asteroids may be carbonaceous (C-Type), metallic (M-Type) silicaceous (S-type) and in composition share features of other space objects.
Occasionally, an asteroid's orbits brings it close to Earth, raising the possibility of an impact. These "near-Earth" objects are monitored in their passage close to the planet. Asteroids also collide with each other, breaking off fragments that can enter Earth's atmosphere as meteors -- the typical shooting star. Asteroids orbiting farther from Earth, such as those in the Trojan belt near Jupiter, pose minimal risk to the Earth.