Definition & Meaning of "[catch] {sb} red-handed"

What is the origin of the idiom "catch someone red-handed" and when to use it?

The idiom "catch someone red-handed" traces its origin to the practice of catching a person with literal blood stains on their hands, serving as irrefutable evidence of their involvement in a crime or wrongdoing. In earlier times, the phrase was associated with catching a thief or murderer immediately after the act, when their hands were stained with the victim's blood. Over time, the idiom evolved to describe any situation where someone is caught in the act of committing an offense or engaging in illicit activities, leaving them with undeniable proof of their guilt.