渣 (zhā): residue

Meanings

Kāfēi zhā kěyǐ zuò féiliào.

Coffee grounds can be used as fertilizer.

Tā shì ge zhānán.

He's a scumbag.

usage

In modern slang, 渣男 (zhānán) means a man who plays with people's feelings, and 渣女 (zhānǚ) is the female equivalent. Very common online.

渣 zhā