Massage that involves genital stimulation, either manually or orally. Erotic massage is usually advertised for in the back of tabloids and locally published magazines.

I don't really know what happens beyond the doors of an establishment that would offer this, but I imagine that you only pay for the service you receive.

Nudge nudge...

Actually, any massage can be erotic, genital stimulation or not.

I have given massages which were utterly platonic and thoroughly erotic; a nice trick if you can manage it. I have also received same from friends, although the eroticism from those was partly from familiarity and partly from the lure of forbidden fruit.

IMHO, touch of any kind can be erotic...it's all in the intent of the giver and desire of the recipient.