Usually, when a man and woman are lying down (or standing) with the crotch area in the face. They lick, kiss, and suck the pussy or dick until desired to stop.
Also used with a woman to woman in where both lick, kiss, and suck eachother's pussy.
Or man to man where both lick, kiss, and suck eachother's dicks.
"We got in the 69 position last night. I was lapping up her pussy while she sucked my dick. It was AWSOME!"