An expression meaning 'I've had enough' or 'no more' — used to say you don't want anything further or can't tolerate something any longer.
もうたくさん！これ以上その話は聞きたくない。
Enough! I don't want to hear any more about that.
掃除はもうたくさんしたから、今日は休もう。
I've cleaned enough, so let's take a break today.
彼のわがままにはもうたくさんだ。
I'm fed up with his selfishness.
もうたくさん食べたから、デザートはいらない。
I've eaten enough already, so I don't want dessert.