I've found guys and girls also tend to have different definitions. As a guy, a thigh gap is the little heart/triangle that most girls can have (if they get in decent shape) just under their hips at the top of their thighs: http://new4.fjcdn.com/comments/Gt+gt+1+just+give+it+time+they+ll+come+they+always+come+_5867a90b3239a5adf0fe2c383328d15a.jpg http://i.imgur.com/QAjb20N.jpg It doesn't even have to be very big: http://www.vinefights.com/wp-content/uploads/2014/04/G4.jpg Usually it comes with fairly fit, athletic legs. For girls, they seem to think of it as a gap from their hip all the way to their knees, and is only achievable with super skinny legs with basically no muscle or fat: https://seeinnerbeauty.files.wordpress.com/2013/10/thigh-gap.jpg https://s-media-cache-ak0.pinimg.com/736x/02/ba/c0/02bac0551ea8dbdf2dc34a0d62ba7530.jpg I vastly prefer the first type, but it seems like most girls are way more obsessed with the second type.