1. an irregular size between small and medium.

2. a adjective referring to clothes that are too small.

An extremely tight, emo or hipster t-shirt. It is irrelevant what size, but mediums and smalls are more likely

–noun
1. any size Medium shirt (especially a T Shirt) worn by a man whose body-size would usually require a size Large shirt for comfort, worn for the accentuating affect it gives to musculature of the torso and arms; The resulting effect is similar to that of a medium-sized person wearing a size Small shirt.

2. a nickname for a man wearing such a shirt