Season finale

A season finale (British English: last in the series; Australian English: season final) is the final episode of a season of a television program. This is often the final episode to be produced for a few months or longer, and, as such, will try to attract viewers to continue watching when the series begins again.
A season finale may contain a cliffhanger ending to be resolved in the next season. Alternatively, a season finale could bring open-ended storylines to a close, "going out on a high" and similarly maintaining interest in the series' eventual return.
Series finale.
The final episode of a television series often concludes the entire premise of the show.
There are examples of episodes, ostensibly having been the "season finale", unexpectedly becoming the "de facto" series finale due to the cancellation of the series. Recent examples of this include "John Doe", "Invasion", "Two Guys and a Girl", "Instant Star", "Las Vegas" and "Everybody Hates Chris".
In sports.
In American English, the term has developed to describe the final event of a sporting season, e.g. in soccer or Motocross, perhaps partly because of the popularity of these with television viewers.