Definition & Meaning of "white rat"in English

What is the origin of the term "white rat" and how is it used?

"White rat" is a slang term for a person considered sneaky, treacherous, or likely to betray others. It appeared in English in the 19th to early 20th century, drawing on the image of rats as secretive and untrustworthy creatures, with "white" perhaps emphasizing visibility or notoriety. The term is used in informal, critical, or accusatory contexts to describe disloyalty or deceit. It is derogatory, context-dependent, and conveys contempt, though it is not vulgar.