When you trick someone into looking in a different direction by saying "Mira ama, una mosca", just to expose their neck so you can suck on it. Similar to a hicky but with the intended target being your own mother.

What you call a girl thats obese, but to your friend "mosca" she would classify as "thicc".

A woman that is clearly obese and in no way, shape, or form desirable by any man but you know for sure your friend ,mosca will hit it