A Jolly Roger is the skull and crossbones flag that flies at the top of a pirate ship.
Although the origin of the name "Jolly Roger" is unknown, one theory attributes it to the use of red flags. A red flag was commonly used during naval warfare centuries ago to signal that no mercy would be shown and that anyone captured would be killed immediately. According to theorists, the French called it a Joli Rogue ("pretty red"), which was then translated into English as Jolly Roger. Another theory holds that the name Jolly Roger was derived from "Old Roger," a term for the Devil. Oh, these pirates are so enigmatic!