dutch/frisian slang for chugging (the remaining of) a glass/bottle of an alcoholic beverage(beer, liquor)
it's a verb, most often used without last n because it's slang
wij hebben geat/we have geat
note: a is pronounced differently in dutch as in english
person 1 is drinking a beer
person 2: atte atte!
person 3 joins in yelling atte
person 1 chugs what's remaining of the beer