the nitty-gritty

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

實質內容, 具體細節, 關鍵之處

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

:
Let's get down to the nitty-gritty of the project.
讓我們深入探討專案的實質內容
He explained the nitty-gritty of how the machine works.
他解釋了機器工作原理的實質內容