Definition
Used when pouring a drink for someone, indicating that they should tell you when to stop.
请说何时停止（倒酒时用）
Let me pour you some wine, just say when.
让我帮你倒些酒，够了跟我说。
The waiter held the coffee pot, asking, 'Would you like more? Just say when.'
服务员拿着咖啡壶问：『您还需要更多吗？够了请说。』
Just say when as I add the milk for you.
我帮你加牛奶，够了跟我说。