There are quite a few objects in the universe capable of causing a really, really bad day on planet Earth, including a wayward comet or large asteroid. Most meteors, however, are not very high on an astronomer's scale of scary extraterrestrial events. There are a number of differences between a comet and a meteor, from their general composition to the roles they play in the universe.
A comet is a celestial object believed to be composed primarily of space dust and frozen gases. Experts think they are born somewhere in the outer parts of the universe and are not related to the formation of our solar system at all. A comet follows an orbit that may bring it close to a star, such as the Sun, and as it approaches the star, a portion of its ice core may melt and release a trail of dust-sized particles. This cycle can continue for millions of years.
A meteor, on the other hand, is a bit of rock or other debris, and it does not follow an orbit around the Sun. It even has a different name while it remains floating in outer space — it's called a meteoroid. It's only known as a meteor when it enters the Earth's atmosphere.
When the Earth passes through a comet's trail or debris field, individual meteoroids hit or skip across the first layers of the atmosphere. Observers on Earth may be fortunate enough to see the last few seconds of the existence of this debris as it streaks across the sky and burns up. Unlike a comet, a meteor will not return a number of years later.
A comet rarely passes within a few million miles of the Earth, while a meteor, by its very definition, must strike the first layers of the Earth's atmosphere. The arrival of a comet can be predicted with some degree of accuracy, and it can rarely be seen with the naked eye. Meteors can enter the Earth's atmosphere at any time of the day or night and during a shower, it is not unusual to see dozens or even hundreds of them within a few hours.
Scientists give comets official names for identification, such as Swift-Tuttle, Hale-Bopp or Halley's Comet. A few large asteroids may receive identifying names as well, but meteors do not. Virtually all of these objects cease to exist once they've entered the Earth's atmosphere, although a rare few make it to the ground. Once it has made contact with the Earth's surface, it becomes known as a meteorite. While a comet may be composed of space dust, organic materials, and ice, most meteors contain elemental metals, such as iron, along with inorganic minerals, such as quartz.