I didn`t know what 'hard capping' was either.
Learn something new everyday !
I think most people`s definitions are based on experiences, rather then what they`ve been taught. Even if you are taught one thing, but experience told you another, then you have both your definition and your working theory.
So each experience a person has, when the body/brain sends that 'omg' signal that a change is occuring,and they realize it`s becoming actual sex..... that tends to implant in the brain, and become the standard people measure by.
When we connect with someone physically, there are all kinds of things that people naturally have to compromise on. I think sex can be a very good measurement on how much people willingly compromise, adjust, exhibit patience, and learn each other. What happens there, will bleed over elsewhere. Both good and bad.