It is a much more invasive pat-down that involves touching, probing, and feeling your body, including your genital area, to determine if you are concealing something.
It is what the Transportation Security Administration (TSA) will do to you if you opt-out of the full body scanner, which takes a naked picture of you, before boarding an airplane.
TSA Agent: "If you won't let me to take a naked picture of you, then I'm going to rub your penis."
Child: "That would be sexual assault."
TSA Agent: "Nonsense, it's just an enhanced patdown. Now spread your legs."