Actually, the answer to your question is more interesting and involved than I had thought:
A "television pilot" (also known as a "pilot", "pilot episode", and "series premiere") is a standalone episode of a television series that is used to sell the show to a television network. At the time of its creation, the pilot is meant to be the testing ground to gauge if a series will be successful, and is therefore a test episode of an intended television series. It is an early step in the development of a television series Television networks use pilots to discover whether an entertaining concept can be successfully realized. After seeing this sample of the proposed product, networks will then determine whether the expense of additional episodes is justified. They are best thought of as prototypes of the show that is to follow, because elements often change from pilot to series. The Variety Magazine estimates that only a little over a quarter of all pilots made for American television proceed to the series stage, although the figure may be even lower.