'Pegging' is a sexual practice in which a woman performs anal sex on a man by penetrating the man's anus with a strap-on dildo. This practice may also involve stimulating the male genitalia. In terms of physical pleasure, a woman's genitals may get direct stimulation from the base of the dildo, or in the case of a double-ended dildo, from vaginal (or internal) penetration.

A woman can use a secondary vibrator, between the dildo and her genitals, to get pleasure from pegging. Men may find stimulation of the anus, rectum, and especially the prostate, pleasurable. During anal sex, male pleasure can be particularly derived from the prostate, which can lead to an orgasm and ejaculation. Some men enjoy masturbating (or being manually stimulated) during pegging. Triple-ended dildos provide both vaginal and anal stimulation of the female partner.

Source: Wikipedia