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Comets
Anyone who's ever seen a comet, its bright tail flickering as it streaked across the night sky, might describe it as a fiery mass. But the exact opposite is true. The nucleus of a comet is made up of densely compacted ice and dust. As a comet approaches the sun, the heat begins melting the ice. Gas and dust, which are released as the ice melts, combine to form a vapor cloud around the nucleus. Meanwhile, some of the escaping gases are stripped of electrons and they're pushed back by the solar wind. The result leaves the comet with a radiant bluish tail. Meanwhile, repelled by the sun's radiation, the loosened dust particles are also forced away from the nucleus, forming a second -- and longer -- tail. It's not uncommon for a comet's tail to span millions of miles. Although all comets are considerably large when they begin their journeys, multiple trips past the sun cause most to shrink over time. Sometimes the stress of the initial fly-by will be enough to break up a comet. But watch out for those that are at their prime fighting weight -- at its core, the famed Hale-Bopp comet is nearly 25 miles wide.
Meteorites
Meteorites, on the other hand, are nowhere near as threatening as comets. In fact, if you ever come across a meteorite, any potential danger it might have posed to Earth will have already passed. That's because a meteorite is any object that originates in space and makes it to Earth intact. And that's no small feat. Every day, tens of thousands chunks of space debris enter Earth's atmosphere, but most burn up before getting anywhere close to terra firma. Those that survive the journey are usually the size of small rocks by the time they touch down. In fact, to the untrained eye, most are indistinguishable from small rocks. It's quite possible you have seen one or more meteorites over the course of your life and didn't realize it.
Similarities
So, in determining how similar a comet and meteorite are, one could understandably conclude they're very much alike. After all, both are products of outer space, and a meteorite could very well be a burned out fragment of a comet. Scientifically speaking, however, the similarities are few and far between. The word "comet" refers to a large mass of ice and dust that travels through space, whereas "meteorite" is defined as an earthbound fossil of what once was a comet, asteroid or meteor.
Bridging the Differences
To get a clearer view of the family resemblance between comets and meteorites, it helps to examine other members of their galactic clan. Asteroids are rocky masses that resemble -- and are sometimes confused for -- small planets. A lion's share of all known asteroids orbit the sun, between Mars and Jupiter, as part of the Asteroid Belt. While they're considered small in comparison to planets, asteroids can still be a healthy size -- the largest known asteroid, Ceres, is 580 miles wide. Meteors are fragments of asteroids or comets that enter Earth's atmosphere. A fragment even as small as a pea will leave in its trail a bright streak of light, which, to further complicate matters, most people refer to as a shooting star. When a dust cloud enters Earth's atmosphere, its particles are known as a meteor shower. The bottom line is regardless of what you call it, a meteor was once either a comet or an asteroid ... and regardless of its origin, it becomes a meteorite once it lands on Earth.