This idiom means to be caught in the act of committing a wrongdoing, with undeniable evidence of guilt. It suggests being apprehended during or immediately after an illicit act, leaving no room for denial, and is often used in contexts of crime, cheating, or mischief to emphasize clear culpability.

The phrase originates from 15th-century Scotland, where ‘red-handed’ referred to being caught with blood on one’s hands after a crime, such as poaching or murder. An early legal use appears in the 1432 *Acts of the Parliament of Scotland*: ‘Taken red-hand.’ By the 19th century, it was metaphorical, with Sir Walter Scott’s 1819 novel *Ivanhoe* popularizing it in English literature. Its vivid imagery of blood-stained hands ensured its lasting use, especially in legal and journalistic contexts.