what is the defenition for astroid?

Answer 1

Asteroids, also called minor planets or planetoids, are a class of astronomical object. The term asteroid is generally used to indicate a diverse group of small celestial bodies that drift in the solar system in orbit around the Sun. Asteroid (Greek for "star-like") is the word used most in the English literature for minor planets, which has been the term preferred by the International Astronomical Union; some other languages prefer planetoid (Greek: "planet-like"), because it more accurately describes what they are.

Answer 2

A stony, less than planetary mass object, circling the sun on a unique orbit. Often from the asteroid belt, but also from the Kuiper belt or the Oort cloud.

Answer 3

Astroid is a type of plane curve:
http://en.wikipedia.org/wiki/Astroid

But, given the topic you're posting to, probably you mean "asteroid":
http://en.wikipedia.org/wiki/Asteroid