The term meteor comes from the Greek word meteoron, meaning phenomenon in the sky. It is used to describe the streak of light produced as matter coming from the solar system falls into Earth's atmosphere creating temporary trails of light due to  atmospheric friction. This phenomena typically takes place at height of 80 to 110 kilometers above Earth's surface.
The word meteroid refers generally to matter revolving around the Sun (or any object in interplanetary space) that is too small to be called an asteroid or a comet and that can produce the phenomena of meteors when falling into the Earth's atmosphere.  Even smaller particles, like dust grains or any interstellar material that happens to enter our solar system can be called micrometeoroids. When the meteorid is big enough to reach the surface of Earth without being completely eaten up by friction, it is called a meteorite.

Why trails of light?

A beautiful meteor
When a meteor enters the atmosphere friction causes ablation of its surface (click here to know more about this process), burning it up. If the meteor is small, it vaporizes before hitting the ground. If the meteor is larger, it survives the impact on the ground, although it will be reduced in size during its passage into the atmosphere.  
But why are meteors accompanied by trails of light? Friction with the atmosphere makes the body  loose its initial kinetic energy, transferring it partly to the air in the form of heat, and partly irradiating it  as light. For this reason, meteors are associated with very brilliant trails of light.


Meteor showers

Meteors often occur in showers: this means that, during certain periods of the year, there is an evident increase in the number of meteors. These periods can last for a couple of weeks, with peaks of a couple days. The reason for these showers is very simple: during their life, comets experiment an important loss of mass, leaving a great amount of debris behind them. Furthermore, comets can break down into fragments, that at first are clustered together as a swarm, then spread out along the old comet orbit. When the Earth passes through the orbit of an old comet it encounters a fraction of these debris and rocks, causing a meteor swarm or a meteor shower. (click here to know more about comets).