In the United States, many series premieres are aired in the fall time or, for mid-season replacements, either in the spring or late winter.
At the time of its creation, the pilot is meant to be the testing ground to gauge whether a series will be successful.
As such, "Pilot" is overwhelmingly the most common title used for a series premiere.
[2] In the case of Firefly, the original pilot ("Serenity") was intended to serve as the series premiere but was rejected by the network, and a new first episode, "Train Job", was shot specifically for broadcast.
Amazing Stories (1985) is credited as being one of the first series commissioned without a pilot.