Someone who either:
1. Is overweight, has a thin/ attractive face, but does a good job at hiding the fact that they are overweight (dark clothes, stripes, dresses).
2. Is of a relatively normal weight but is in the process of gaining weight.
3. Is of a relatively normal weight but has the genetic potential to gain weight (mother or father is overweight/obese).
Don't hook up with her, she's totally a Crypto-fat. She looks great in the dark but she hides her wide load well.