is the practice of stimulating the man's penis solely through use of the woman's vaginal muscles.

Use of the vaginal muscles to milk the penis. Linguistically, this is a French corruption (via the Portuguese) of the original Tamil place-name Pahmpur or Pampur, which is the Dravida Kurumba Pulayam city where this esteemed practise originated.
Thus, 2 scholars note: "POMPOIR POWER: The voluntary control of the circumvaginal muscles during sexual intercourse is known as pompoir ("pahm-pour") in the Tamil language of Southern India. According to authors Herbert & Roberta Otto, a popular mythology developed around this ability in the United States between 1930 & 1950. Popular sexual literature made much of this ability under the name 'snapping pussy,' which in the South was called 'snapping turtle.'" ('Sexual Energy Ecstasy: A Practical Guide to Lovemaking Secrets of the East & West' David & Ellen Ramsdale. NY: Bantam Books, 1993, p 91)

Also, "The strength of a woman's vaginal muscles count much more than the size of her vagina. In Asia & elsewhere, skilled female lovers developed their PC muscles to the point where they could grip, milk, & make any man's penis orgasm without any other movement.// The Tamils of Southern India called this skill of vagina muscle control pompoir. In the Arabic world, a woman who had mastered the use of her PC muscles during sex was the...