A small body made of ice, dust, and rocks which orbits the sun: A comet can be a collection of gas, dust, and volatile ice that travel around the sun, generally in very eccentric orbits.

The source of such bodies may be the oort cloud (cloud of comets).

A comet, probably resembling a "dirty snowball", can be between 0.1 and 100 kilometers across, which travels through the solar system in an ecliptical orbit of random inclination to the ecliptic.

A comet grows a tail if it goes close enough to the sun.