Technical term in astronomy for a small rocky or metallic body in outer space, smaller than an asteroid. Compare 流星物質 (meteoroid material).
See also: 流星物質
When a meteoroid enters the Earth's atmosphere, it is observed as a meteor.
小惑星 is an asteroid, generally larger than a meteoroid.
Compound of 流星 (meteor) + 体 (body), a straightforward calque of the English 'meteoroid'.