stay in 留在某处

stay in something 表示“留在……的内部”，相反 stay out 表示“不进入某处，留在外面”。

例句：

We'll stay in the car. I'll be right back.

你们待在车里。我去去就来。

I can stay out as late as I want.

我可以一直待在外面，想几点回去就几点回去。

It's best you stay in there.

你能留在这里简直太好了。

Let's stay outside for a while.

我们出去待一会儿吧。

对话：

A: Look at that rain. I'm going to stay in today.

瞧瞧这雨，我今天要在屋里待着。

B: Me too. I don't want to get wet.

我也是，我可不想变成落汤鸡。