Literally: bright – mirror – stop – water
Alternately: Like a polished mirror. Like still water. Clear and serene. Specifically, a placid mental state that results from a mind free of ill-will or wicked thoughts. The calm of the just.
Notes: There are apparently some who write 名鏡 (“famous mirror”) instead of 明鏡 (“flawless mirror”). This is an error.
This compound apparently comes from the Zhuangzi – “one of the two foundational texts of Daoism.”