Pronounced like molasses (muh-las-iz), it is someone who has a small or below average sized ass. It isn't a medical diagnosis, it is simply the fact that someone has a small ass. It can be used as a name to call someone with a small ass, like a nickname, or it can be used to describe the person's ass directly. When figuring out if someone has smallasses, you only take the size of the butt cheeks into account. Quality and color of the ass are not relevant, nor is the gender of the person. You don't need to see their bare ass cheeks to make the decision that they have smallasses either. Simply giving them a friendly grope can help you determine. Typically, if you can fit most of one of your hands around one of their butt cheeks, that is a good sign of smallasses.
Hey, smallasses! Get over here!
I walked past Tim today on the way to close and I noticed he had smallasses.