A masseur is a man whose job is to give massage. He uses his hands to press and move your muscles, so you feel less tight or less sore. The word is French. In careful English, masseur is a man and masseuse is a woman. Though actually, many people today prefer massage therapist for both, because the old pair can feel dated, and in some places masseuse has been used for shops that are not really about health. You still hear masseur in hotels and spas, and in older books. It is an ordinary job word — not slang, not very formal.