What is the difference between a comet, an asteroid, a meteor, and a meteorite?

Asteroids are rocky or metallic bodies, most orbiting between Mars and Jupiter in the main belt, and they are essentially leftover building material from the formation of the solar system. Comets are mixtures of ice, dust, and rock originating in the outer solar system, and when their orbits carry them close to the sun the ice sublimates, releasing gas and dust that forms the glowing coma and the tail, which always points away from the sun rather than trailing behind the direction of travel.

The other two terms describe stages of the same event rather than different objects. A meteoroid is a small fragment travelling through space. When it enters Earth's atmosphere and the compression of air ahead of it heats it to incandescence, the visible streak is a meteor, commonly called a shooting star. If any of it survives the passage and reaches the ground, that surviving piece is a meteorite. So the same object can be a meteoroid, then a meteor, then a meteorite within a few seconds.

Two practical notes. Meteor showers occur when Earth passes through a debris trail left by a comet, which is why they recur on predictable dates each year, with the Perseids in August and the Geminids in December among the most reliable. And planetary defense is a real field: NASA's DART mission in 2022 deliberately struck the small moon Dimorphos and measurably changed its orbital period, demonstrating that a kinetic impactor can alter an asteroid's trajectory. Surveys tracking near-Earth objects have catalogued the large majority of the biggest ones, and none currently known poses a significant impact risk within the next century.