Erogenous zones refer to areas of the body that are highly sensitive and pleasurable when touched. The term was used by one of the earliest sex researchers, Havelock Ellis, to describe small areas on the body that could produce an orgasm when "simple pressure" was applied. It's come to be synonymous with the idea of a sexual hot spot, a part of the body that produces intense pleasure when stimulated.
Common areas that are considered erogenous zones include the lips, tongue, palms, fingers, soles of feet, inner thighs, nipples, neck, ears, armpits, and the genitals. While it's true that for most people there are parts of the body with higher concentrations of sensory nerve receptors, individually, there's no way of knowing if a particular area will be pleasurable without either asking, or testing it out. As such, we might think of individuals as each having their own erogenous zones, but the idea of there being standard erogenous zones that can be categorized by sex or gender or star sign, zones that everyone in a group will find pleasurable is less accurate.