On a dark night when looking up, every so often a streak of light may be seen travelling across the sky for a brief instant. This streak of light is called a meteor. Other popular names are "falling star" or shooting star". The average meteor is not very bright and is produced when a small piece of natural space debris, about the size of a grain of sand, enters the Earth's atmosphere and burns up due to friction with the Earth's atmosphere. This piece of material is called a meteoroid. Anywhere from 2 to 10 or more meteors may be seen per hour as these meteoroids, which have been travelling in space, chance to collide with the Earth.
More meteors are seen in the early hours of the morning than in the evening hours. This is because in the evening, the Earth, in its orbital motion around the sun, is heading away from the average meteoroid, whereas in the morning it is heading into the direction you are looking and thus sweeps up more meteoroidal debris.
The average meteor will be within the brightness range of the stars that are normally seen. Occasionally, however, the Earth may encounter a much larger than normal meteoroid, and this will produce a very bright meteor. When the brightness magnitude of the meteor exceeds the brightness of Venus at its maximum brilliance (mag < -4), the meteor is called a fireball. A very bright fireball might be produced by a meteoroid a metre or more in diameter and weighing several tons.
Meteoroids come in all shapes and sizes. They may range from a millionth of a metre in diameter to several metres in diameter. The smaller sizes are a lot more common than the larger sizes. Occasionally, if the meteoroid is large and massive enough, and if entry conditions are favourable, not all the meteoroid is consumed in the burn-up or ablation process, and a fraction of the meteoroid may make it all the way down through the atmosphere to the surface of the Earth. The piece of rock that survives is then called a meteorite. The mass of the meteorite will in general be less than 1% of the mass of the original meteoroid.
When they reach the Earth's upper atmosphere, meteoroids have velocities between 11 and 72 km/sec. The average meteoroid will burn up at an altitude of between about 80 to 120 km. A large fireball may make it down to 50 or even as low as 20 km. It is interesting to note that the meteoroid does not lose much velocity until most of its mass has been ablated away. Some bright meteors or fireballs may explode at the end of their travel. This occurs because the atmospheric decleration pressure exceeds the internal strength of the material and it implodes. This can cause a spectacular sight.
A meteoroid that is large enough to "drop" a meteorite will usually suffer all its ablation above about 20km. By this point most of its space velocity has been lost, and the resultant meteorite will "drift" down to Earth at a terminal (falling) velocity of only about 100 metres/second.
So in summary, the term meteoroid is used to describe a small body as it travels through interplanetary space. The word meteor on the other hand, refers to the phenomenon that occurs when such a body encounters the atmosphere. And if any part of a meteoroid survives the atmospheric entry process and hits the planet's surface, it is called a meteorite.