If you graduated high school, or may be simply scientific-minded, you can notice, that Ass to mouth generally excludes cleaning the penis or other object (turn on your fantasy! ;) ) after its removal from the anus and before its insertion into the mouth for the sake of increased sexual excitement. OK, I don’t mind.
One girl is cool. Fuck girl in ass and mouth even cooler! But what’s about if there is a few girls??? Yees, MO-O-ONSTEER sex :) Variant of A2M, where cock is moved from one girl’s (or partner, if you want) ass to a different girl’s mouth is known as A2OGM or ATOGM – Ass To Other Girl’s Mouth. Or sometimes A2OM(what’s the abbreviation? ;) )
Have a look on A2M example :)