Meaning:

“潜” means “under the water,” and “规则” means “rules.” In contrast to “explicit rules,” this Chinese term refers to “implicit rules,” which are unwritten rules widely accepted and functioning in the society. In many instances, “implicit rules” can be another word for “underhanded deals,” like a salesperson of second-hand cars often overcharging clients, and some actresses sleeping with directors or producers to get a role.

Example:

A: 听说你打算买辆车？

Tīngshuō nǐ dǎsuàn mǎi liàng chē？

Are you planning to buy a car?

B: 是啊，我想买辆二手车来代步，但又害怕遭遇潜规则买到问题车。

Shì a，wǒ xiǎng mǎi liàng èrshǒuchē lái dàibù，dàn yòu hàipà zāoyù qiánguīzé mǎi dào wèntíchē。

Yeah. I want to buy a used car for daily use, but I am deterred by the “implicit rules” in this trade, and fear that I might buy a problem car.