A meteoroid (/mitird/) is a tiny rocky or metallic body that flies through space.

Meteoroids are much smaller than asteroids, ranging in size from a few grains to objects about one meter in diameter. Micrometeoroids or space dust are objects that are smaller than this. The majority of them are comet or asteroid fragments, but some are collision impact debris expelled from planets like the Moon or Mars.

When a meteoroid, comet, or asteroid reaches Earth’s atmosphere at speeds of more than 20 km/s (72,000 km/h; 45,000 mph), the object’s aerodynamic heating creates a streak of light, both from the glowing object and from the trail of glowing particles it leaves behind. A meteor, often known as a “shooting star,” is a natural occurrence. When meteors reach a height of roughly 100 kilometers above sea level, they become visible. A meteor shower is a group of meteors that appear to come from the same fixed location in the sky and appear to occur seconds or minutes apart. A meteorite is the remnants of a meteoroid that has hit the ground after its surface material has been abated during its passage through the atmosphere as a meteor.

Each day, an estimated 25 million meteoroids, micrometeoroids, and other space debris enter the atmosphere, resulting in an estimated 15,000 tonnes of debris entering the atmosphere.

A meteoroid was described by the International Astronomical Union (IAU) in 1961 as “a solid object traveling in interplanetary space, having a size substantially less than an asteroid but significantly bigger than an atom.” Beech and Steel suggested a revised definition in the Quarterly Journal of the Royal Astronomical Society in 1995, stating that a meteoroid should be between 100 m and 10 m (33 ft) wide. To retain the difference, Rubin and Grossman recommended a modification of the prior definition of a meteoroid to objects between 10 m and one meter (3 ft 3 in) in diameter in 2010, following the finding of asteroids smaller than 10 m. The minimal size of an asteroid, according to Rubin and Grossman, is determined by what can be seen from Earth-bound observatories. Thus the difference between meteoroid and asteroid is hazy. 2008 TS26 with H = 33.2 and 2011 CQ1 with H = 32.1, both with an estimated size of one meter, are two of the tiniest asteroids found (based on absolute magnitude H) (3 ft 3 in). The International Astronomical Union (IAU) revised its definition in April 2017, restricting size to between 30 m and one meter in diameter but allowing for a departure for any object that causes a meteor.

Micrometeoroids and interplanetary dust are objects that are smaller than meteoroids. The word “meteoroid” is not used by the Minor Planet Center.

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