A TV show's pilot episode is a stand-alone episode intended to pitch the show to a network or distributor. A pilot episode acts as a testing ground to ascertain whether a series would be successful.

Martin Clunes has spoken about the ‘abandoned’ first episode of Men Behaving Badly that never made it to screens. Running for ...

For example, the original pilot did not convey that Cersei and Jaime are twins, so when they are caught having sex at the end of the episode, it just seems like an affair rather than a major shock.