Darts are missile weapons, designed to fly such that a sharp, often weighted point will strike first. They can be distinguished from javelins by fletching (i.e., feathers on the tail) and a shaft that is shorter and/or more flexible, and from arrows by the fact that they are not of the right length to use with a normal bow.

The term has been used to describe an extremely wide variety of projectiles, from heavy spear-like ammunition for siege engines or atlatls to tiny poisoned needles for use in blowguns. (source)