This is different than a rimjob. A rimjob would, however, be a precursor to anilingus. It is the act of plunging one's tongue into the anal cavity of your sexual partner and then swirling and thrusting aforementioned tongue in an effort to make said partner happy.
It is well advised to wash the anus that is to be pleasured thoroughly (and perhaps even douche) before attempting this.
After a thorough scrubbing, he performed analingus on her.