Cupping involves placing a number of glass 'cups' on the body. The cups themselves are often spherical in shape. The air inside the cup is heated and the cup is then placed against the skin making an air-tight seal. As the air inside the cup cools, the reduced pressure in the cup sucks against the skin.
When combined with use of massage oil, the cups can be slid around, producing a pleasant 'negative pressure' massage effect.
In therapeutic use, cupping is a very quick procedure lasting only a few minutes. Any after-marks on the skin disappear after half an hour.