flagellant:
(plural: ‘flagellants‘; pronunciation: the letter ‘g’ is said with a ‘j’ sound, as in “judge” — for the right pronunciation, please click here)

a female flagellant whipping her partner
a person who whips him/herself as a religious punishment;
a person who beats himself/herself, beaten by others or beats others with a whip in order to get sexual pleasure,

religious flagellants whipping themselves in repentance
John, my classmate, is a flagellant who whips and cuts himself for the imaginary sins he’s committed in his day-to-day life.
Almost every religion in the world seems to have a sect of flagellants that go about in processions on some specific days as a sign of repentance and purification.
Those Italian flagellants in the mid of the 14th century had no idea that bubonic plague, also known as Black Death, that had killed thousands of people was just a disease carried by rat fleas from China, and instead of beating themselves to death, they could have taken proper hygiene measures and some simple medical treatment which might have saved some of their folks.
It is still a mystery for the psychologists and experts in sex why sex flagellants need to be whipped or spanked or why they need to whip or spank their partners to get sexual satisfaction.
