An exclamation meaning 'I can't do it anymore' or 'I've had enough'; used when one feels unable to continue. Casual, everyday expression.
宿題が多すぎて、もう無理だよ。
There's too much homework; I can't handle it anymore.
会議が長すぎて、もう無理…寝そうだ。
The meeting is too long — I can't take it... I'm about to fall asleep.
このプロジェクトは期限内に終わらせるのはもう無理です。
It's impossible to finish this project within the deadline now.
『もう無理！』と叫んで部屋を出た。
He shouted, 'I can't take it anymore!' and left the room.