This definition comes from a partner of mine. It isn't perfect, but it encompasses a lot of activities that commonly get called "sex" but with qualifiers, like oral sex, group sex, cyber sex, etc. Unfortunately, it's also not the definition most people use. In perhaps 75-90% of usage I encounter, "sex" means male-female genital-genital penetrative intercourse. The bulk of the remainder include anal sex and an unspecified number of girl-girl interactions, neither of which are particularly relevant in contexts where I'm participating in the conversation.
That said, what other terms best convey the idea of all sorts of directed erogenous touching (including that one, which is so clinical as to either confuse people or drive them to laughter or rejection or both)? I've heard "sexy times", "sex-y play", "sexual play", "erogenous stimulation". What else is out there? Are there other subsets of sexy times that can be conveyed succinctly?
I ask this not entirely out of academic interest. My personal bedroom proclivities tend toward second and third base. That isn't normal, and is a relatively important factor in a lot of ways, so in the context of a casual conversation leading towards play I am always looking for better ways to get my meaning across unambiguously without sounding too clinical.