An enema is the procedure of introducing liquids into the rectum and colon via the anus.

Recreational usage

The paraphilia directed towards enemas is known as klismaphilia, the enjoyment of enemas.

Enemas may be used as part of BDSM activities, or as a regular sexual activity for an individual or between partners. Enemas can be pleasurable to either sex, and in males, enemas can stimulate the prostate gland. Unexpected erections are common in medical settings, even if the person would otherwise consider it an unpleasant procedure.

An enema may also be used prior to anal sex or anilingus in order to enhance the sensation of intercourse, or to remove feces prior to sex, possibly reducing bacterial transmission and risk of infection, or just to reduce the possibility of fecal material or detritus from sexual activity adhering to the genitals or sex toys used during the subsequent activity. Enemas used for anal sex should not be used consistently and enema bottle contents should be removed and replaced with simple luke-warm water. Continual usage of enema solution may be harmful for the anal cavity.

(source: WiKiPedia)