Meteoriod is probably the most accurate term. (Same source defines "asteroid" as being between several kilometers and several hundred kilometers in diameter.) It's like the distinction between "ship" and "boat".
meteoroid (mê´tê-e-roid´) noun
A solid body, moving in space, that is smaller than an asteroid and at least as large as a speck of dust.
The American Heritage® Dictionary of the English Language, Third Edition copyright © 1992 by Houghton Mifflin Company. Electronic version licensed from INSO Corporation; further reproduction and distribution restricted in accordance with the Copyright Law of the United States. All rights reserved.
How big does a sail boat have to be before it becomes a ship?
A friend of mine is buying a 118' sail boat.
He didn't know the answer.