A space between a girl's upper thighs that can be seen when she is standing if she is thin. This is often an excellent indicator of the rest of the girl's body, as if a girl has upper thigh clearance (or, for short, "UTC") then she is likely thin everywhere else. Absent upper thigh clearance, you are taking a risk that she's a chubster. Note: This phrase is also referred to as "inner thigh clearance"
Wow - I guarantee that girl has a slamming body. She has at least 1 inch of upper thigh clearance - a sure sign of thin legs and a tight ass.