This page contains information regarding Star Trek: Discovery, and thus may contain spoilers.
Planetoid was the common designation for a small planetary body orbiting a star. These planetoids, or minor planets, could maintain their own individual and unique solar orbit, or they could also be found among asteroids in an asteroid belt.
Several planetary classifications have been applied to these bodies including:
Spock once described Gamma Canaris N as "more than an asteroid. Like a small planetoid, I should say." He further described it as "possibly a remnant of a planet breakup." This planetoid was unique due to the fact that it had an atmosphere "practically identical to Earth," as well as a gravity similar to Earth, which was "most unusual for its size." (TOS: "Metamorphosis")