the nitty-gritty

US /ðə ˈnɪt.i ˈɡrɪt.i/
UK /ðə ˈnɪt.i ˈɡrɪt.i/
"the nitty-gritty" picture
1.

实质内容, 具体细节, 关键之处

the most important aspects or practical details of a subject or situation

:
Let's get down to the nitty-gritty of the project.
让我们深入探讨项目的实质内容
He explained the nitty-gritty of how the machine works.
他解释了机器工作原理的实质内容