To suck freshly ejaculated semen from any orifice, usually the anus.
From the Chuck Palahniuk
book: "Invisible Monsters"
'"Felching," I lower my voice. I'm calm now. "Felching is when a man fucks you up the butt without a rubber. He shoots his load, and then plants his mouth on your anus and sucks out his own warm sperm, plus whatever lubrication and feces are present. That's felching. It may or may not," I add, "include kissing you to pass the sperm and fecal matter into your mouth."'