(also jack ˈshit taboo ) [U] (NAmE, slang) (usually used in negative sentences 通常用于否定句) anything or nothing at all 丝毫，根本，一点儿（不）
You don’t know jack.
你什么都不知道。
nothing:
I know jack about fashion, but I know what I like to wear.
There’s jack shit to do here.