What is a comet? How do they differ from asteroids?
A comet is an icy body with an eccentric orbit.
Comets are not cry bodies which tend to have highly eccentric orbits. Their orbital periods are often many decades. When they approach perihelion, the Sun vaporizes the comets ices to form the characteristic tail. The ices then freeze and the comet becomes almost invisible as it heads back to the outer solar system.
Asteroids tend to have much less eccentric orbits. Many exist in the asteroid belt which lies between Mars and Jupiter. Asteroids can also be icy but they don't get close enough to the Sun for a tail to form.