A duel between three people is called a ‘truel.’
There have been many famous duels throughout history, many of them by significant persons when it was considered an honorable thing to do. Andrew Jackson is infamous for his duels, particularly for always wining, and Alexander Hamilton died after being shot in one.
But have you ever heard of a three-man duel? The procedure for a truel, if you ever find yourself in one, is simple. Players walk an appropriate distance away from each other and then turn to face. After that, it’s mostly common sense: shoot the other guys before they shoot you. The earliest known truel appears in A. P. Herbert’s play “Fat King Melon” in 1927, and while they’re not exactly common, several are reported to have occurred.
In film the idea was used fairly often such as in “The Good, the Bad and the Ugly,” and the movie “Resovoir Dogs,” in which the three main characters duel each other simultaneously and only one survives. It was not until 1967 that the name “truel,” was actually used.