A can or bottle of beer stored in one's back pocket intended for protection and/or future consumption, usually in a party setting. see also: Double-ass beer and rear-beer

Got the covid-19 vaccine

beer drank after being poured down someone else butt crack

the last sip of beer in a bottle or can...

when a bunch of fucking idiots like steve-o did in jack ass 2 have beer put into their asses, but when it come out the ass someone has to drink it, ass-beer.

often a dare to do the above

or, when you cum in a girls ass then someone drink your cum out of her ass, usually done when there are multiple partners.