This is easy to understand, and it can also be called clean crotch. Generally speaking, it means that the heel of the thigh is facing up, and the hip does not have this texture. For example, there are pantyhose that sell abdomen and buttocks. The buttocks have tight texture, some places have relaxed texture, some places have vertical lines, and some places have horizontal lines, so as to play a role. Flat hips don't have these textures, and the whole thigh is the same as the legs, and there is no texture. In fact, whether it is flat crotch has no effect on wearing. The so-called pantyhose with belly and hip is just a marketing behavior, which is no different from the crotch, but slightly thicker. This aspect really doesn't need to be considered. But I usually try to buy a flat crotch, which makes me feel more comfortable. I hope I can help you. Ask me if you have any questions.