A type of oral sexual intercourse performed by someone actively thrusting their penis into their partner's mouth and possibly their throat.
The distinction between fellatio and irrumatio is based on who is actively moving: irrumatio means to thrust the penis into the partner's mouth, while fellatio means to move the head and mouth up-and-down around the penis.
The word comes from the Latin irrumāre, which had the same definition; although to the Romans it specifically connoted non-consensuality, which is not always the case in English.
