"Don't forget" 用英语可以说成 "don't forget"。这是一句常用的英语短语，意思是提醒对方不要忘记某件事。

例句：

Don't forget to turn off the lights before you leave the house. (别忘了在离家前关掉灯。)

Don't forget to bring your umbrella with you. It's going to rain later. (别忘了带上雨伞，以后会下雨的。)

"Don't forget" 来自于英语动词 "forget" 的否定形式。"Forget" 意思是 "忘记"，而 "don't" 是 "do not" 的缩写，表示否定。因此，"don't forget" 的意思就是 "不要忘记"。