Definition & Meaning of "in deep shit"in English

What is the origin of the phrase "in deep shit" and how is it used?

In deep shit is a slang phrase that appeared in mid-20th-century English to describe being in serious trouble or facing severe consequences. The phrase comes from imagining someone literally submerged in feces—the deeper you are, the harder it is to get out—making it a strong visual metaphor for being trapped in a bad situation. Historically, it was informal and coarse, used to stress severity or danger, and today it remains vulgar but common, mainly in casual, emphatic, or humorous speech rather than polite or formal contexts.