The fly pass pattern is a passing route in which the receiver runs straight towards the end zone without stopping or turning to receive a pass from the quarterback. The Fly route can also be called the go route or the streak route, and it is considered to be one of the routes in football's route tree.
As in any pass pattern, the fly requires receivers to separate themselves from defenders to get free and receive a pass, which can require a variant set of skills depending on which pass pattern is being run. For the Fly pattern, the most important aspect is the receiver's pure speed, but others such as awareness and other football fundamentals are also necessary.
The goal is to separate from the defender by running faster than him, while still being balanced enough to catch the quarterback's pass. The receiver running the fly route will usually be defended by the cornerback, which is logical given that cornerbacks are generally the fastest players on the defensive team and the receiver running the fly route is the fastest player on the offensive team.
The Fly pattern is used in situations where teams find themselves in a position where it is necessary to advance a long distance, usually bigger than 10 yards. The Hail Mary, one of football's most frantic and exciting plays, involves several players running fly routes in order to have many deep passing options on the endzone.