This idiom means to waste time or effort on a hopeless or already resolved issue, persisting in a futile endeavor. It suggests that further action is pointless, like flogging a horse that’s already dead, and is used to criticize stubbornness or redundancy in arguments or tasks.

The phrase likely originated in 19th-century America, tied to rural life and the imagery of a dead horse. An early use appears in an 1859 *London Times* article, describing a politician ‘flogging a dead horse.’ It gained prominence in the U.S. during debates over slavery, where opponents were accused of beating a dead horse.

By the late 19th century, it was common in English, with Mark Twain and others using it to mock pointless persistence.