What is a Pilot ? :

What is a television pilot ? : 

  "Television pilot" (also known as a "pilot" or a "pilot episode") 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 whether 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, much like pilot lights or pilot studies serve as precursors to the start of larger activity, or pilot holes  prepare the way for larger holes.

  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 prototypes of the show that is to follow, because elements often change from pilot to series. Variety 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.

   Most pilots are never publicly screened if they fail to sell a series. If a series eventuates, pilots are usually – but not always – broadcast as the introductory episode of the series.