تعریف و معنای "[buy] a lemon"

What is the origin of the idiom "buy a lemon" and when to use it?

The idiom "buy a lemon" originates from the early 20th century, where "lemon" was a slang term used to describe a faulty or defective vehicle, especially a used car. This phrase is used to describe the act of purchasing something, especially a big-ticket item like a car, that turns out to be faulty, defective, or of poor quality, leading to disappointment and regret.