A trident is a pole with a metal triple-bladed fork at the end, much like a pitchfork, but with straight blades.
The trident has long served as a symbol for the ocean, and for the oceanic gods, such as Neptune. This comes from its initial use as a fishing tool. The trident is far superior to a spear for fishing. The three separate blades give the fisherman a much better chance of skewering a fish than a normal spear ever could. The trident has kept its water association even though centuries have passed since it was used in this manner.
The trident has also served as a weapon. In the real world tridents were used mostly by peasants, as it is a simple weapon to construct, and has a similar feel to the pitchfork that most farmers are intimately familiar with. Organized troops never fought with tridents. Due to the weapons oddity, it gained some popularity in ancient gladiatorial combats. Unusual weapons always helped to draw a crowd, and the trident was no exception.
Fantasy fiction and role-playing games is where the trident really shines. As it is the preferred weapon of most undersea races, such as locathah, mermen, sahuagin, and tritons. While many of the gods and demons of the fantasy worlds have been known to wield a trident as their preferred weapon.
The name trident has also been used as a brand name for a variety of modern day items. Items such as nuclear warheads, chewing gum, computer parts, video game controllers, SCUBA gear, flat panel displays, and even a Junior College all bear the trident name.