A small piece of cometary or asteroidal debris in orbit around the Sun. The meteoroid becomes a "meteor" as it enters our atmosphere and becomes a "meteorite" if it reaches the Earth. The difference are both semantic and physical, since all three terms designate different stages of life of the same object.
A small (1 km) natural object whose orbit around the sun may cause it to collide with other planetary bodies. The term meteoroid is usually used to describe the rocky core of a meteor, while the term meteorite is used to describe the object once it is on the ground.
These are small objects which are believed mainly to come from asteroids and comets. They come in two main types, stony and iron, with some intermediate. Sometimes a meteoroid will cause a flash in the night sky as it burns up on entry, these are known as meteors. Showers of meteors are often associated with comets since they often occur as the earth passes across the orbit of a comet. If a meteoroid hits the earth, it is known as a meteorite.
Tiny sand, or rock sized fragments of cometary debris in our Solar System. When one hits the Earth's atmosphere, it burns up and partially or completely vaporises leaving a trail of glowing vapour known as a shooting star, or meteor. If part of the meteor / meteoroid hits the ground, it is called a meteorite.
A solid object moving through interplanetary space of a size considerably smaller than an asteroid and considerably larger than an atom or molecule. When the object glows while traveling through the Earth's atmosphere, it is called a meteor; when it reaches the surface of the Earth, it is called a meteorite.
A meteoroid is a relatively small (sand- to boulder-sized) fragment of debris in the Solar System. When entering a planet's atmosphere, the meteoroid is heated up by ram pressure and partially or completely vaporizes. The gas along the path of the meteoroid becomes ionized and glows.