Definition (空间)
A very small opening or narrow gap.
（只）留一条缝
She opened the door just a crack so she could hear what was going on outside.
她把门打开一条缝，这样她就能听到外面的动静。
I left the window open a crack to let some fresh air in.
我把窗户开了一条缝，让一些新鲜空气进来。
He opened the box a crack to peek at what was inside.
他把盒子打开一条缝，偷看里面有什么。