An asteroid is a small, rocky (or rocky/metallic) object that orbits the Sun; in a telescope it usually looks like a point of light. Most asteroids are found in the asteroid belt between Mars and Jupiter.
A comet also orbits the Sun, but it is made largely of ice and dust. When a comet nears the Sun, that ice and dust can vaporize, so the object often looks fuzzy and may show a tail—unlike a typical asteroid.
Source: What’s the Difference Between Asteroids, Comets and Meteors? — NASA