Adult falcons have thin tapered wings, which enable them to fly at high speed and to change direction rapidly. Fledgling falcons, in their first year of flying, have longer flight feathers, which makes their configuration more like that of a general-purpose bird such as a broadwing. This makes it easier to fly while learning the exceptional skills required to be effective hunters as adults.
The falcons are the largest genus in the Falconinae subfamily of Falconidae, which itself also includes another subfamily comprising caracaras and a few other species. All these birds kill with their beaks, utilizing a "tooth" on the side of their beak — unlike the hawks, eagles and other birds of prey in Accipitridae, which use their feet.
Peregrine falcons have been recorded diving at speeds of 200 miles per hour (320 km/h), making them the fastest-moving creatures on Earth. Other falcons include the gyrfalcon, lanner falcon, and the merlin. Some small falcons with long narrow wings are called hobbies, and some which hover while hunting are called kestrels.
As is the case with many birds of prey, falcons have exceptional powers of vision; the visual acuity of one species has been measured at 2.6 times that of a normal human.
The traditional term for a male falcon is tercel (British spelling) or tiercel (American spelling), from Latin tertius = third because of the belief that only one in three eggs hatched a male bird. Some sources give the etymology as deriving from the fact that a male falcon is approximately one third smaller than the female (Old French tiercelet). A falcon chick, especially one reared forfalconry, that is still in its downy stage is known as an eyas  (sometimes spelt eyass). The word arose by mistaken division ofOld French un niais, from Latin presumed nidiscus ("nestling", from nidus = nest). The technique of hunting with trained captive birds of prey is known as falconry.