“AA制” in English means "split the bill (evenly)" (各人平均分擔所需費用)
For example if you to eat dinner with a group of friends and then each person pays for a part of the meal, you can tell your friends, "Let's split the bill". In English when we say "split the bill" it usually means to split the cost of the bill evenly amongst everyone, regardless of what each person ordered.
Another similar term is: "Let's go Dutch"
It is similar, but a little different, in that it does not mean the bill is split evenly. It means each person pays for themselves. (各付各的)