No, the phrase isn't some sort of sexy marketing ploy: Erogenous zones are real. They're areas of the body that aren't necessarily o or always sexual by nature but, when stimulated, can cause sexual arousal or pleasure.
Interestingly enough, the reason why these hotspots exist isn't crystal clear. Studies have shown that nipple stimulation lights up the same area of the brain—called the genital-sensory-cortex, the "reward center"—that senses contact with the genitals. This could be what's happening in other erogenous zones as well, but we don't have much evidence beyond that.