Definition & Meaning of "curtain lecture"

What is the origin of the idiom "curtain lecture" and when to use it?

The idiom "curtain lecture" is thought to have originated in the 17th century, when it was believed that wives would give their husbands lectures while they were getting ready for bed. The term is believed to be a reference to the fact that the curtains were drawn in the bedroom, creating a private space for the wife to talk to her husband. is used to describe a private conversation, often of a critical nature, between spouses. It usually occurs behind closed doors, symbolized by the reference to "curtains." The phrase "curtain lecture" is informal and is less commonly used in modern times.