Irrumatio (also known as irrumation or by the colloquialism face-fucking) is a form of oral sex in which someone thrusts his penis into another person's mouth, in contrast to fellatio where the penis is being actively orally excited by a fellator. The difference lies mainly in which party takes the active part. By extension, irrumatio can also refer to the sexual technique of thrusting the penis between the thighs of a partner (intercrural sex).[1]
In the ancient Roman sexual vocabulary, irrumatio is a form of oral rape (os impurum), in which a man forces his penis into someone else's mouth, usually a woman's.[2]