These are younger, smaller companies with a size of $250-$1 billion dollars. You might have heard of a few, but not as many: Caterpillar, Comcast, Ethan Allen Interiors, Universal Electronics.
Micro Cap
These are the smallest, emerging companies with market capitalization under $250 million. Probably you have not heard of most of these companies: Wet Seal, Finish Line, Krispy Kreme Doughnuts.