Girls who are NEITHER really skinny or fat...but somewhere in between. Skinny-fat girls usually wear clothes that are TOO small for their 'not so skinny' bodies. A skinny-fat girl usually may wear a pair of low-rise jeans that are WAY too tight causing her fat to spill out of the top of her pants.
-"Oh mah gawd Becky!!! Look at Lisa...did she lose weight???"
-"Yeah, it totally looks like she lost a little bit of weight...but she still looks skinny-fat to me! I mean ewww look at her fat jelly rolls hanging out of her jeans!"