Slapping refers to giving an open palm strike to the face of a slave. In normal society and behavior, slapping someone is usually not acceptable, and this is one of the reasons why it is a fetish for some Masters or Mistresses. The power to slap their slave or discipline them as desired can cause a powerful arousal.
The face is a very sensitive part of the body, and normally only light slapping is permitted. At no times should the Master or Mistress strike hard enough to cause bruising or other marks unless this has been agreed during the booking.