Fear play describes any sexual activity that involves the use of fear to bring about sexual arousal.
In fear play, an individual's terrified mental state triggers a rush of adreline which causes arousal. Fear play is different from masochism, in which arousal is caused by an endorphin rush.
Fear play falls into a category of BDSM-related activities, marked by high physical or psychological risk, called "edge play."
More About Fear Play
Some forms of fear play may take advantage of a person's pre-existing emotional doubts and fears, of abandonment or humiliation for example, while others work on a physical level. Physical forms of fear play include medical play, knife play, and kidnapping.