Wiktionary
series finale
n. The promotional or advertisement term used to describe the final episode of a television program, usually a situation comedy or a drama.
Wikipedia
Series finale
A series finale refers to the last installment of an episodic entertainment series, most often the final episode of a television series. It may also refer to a final theatrical sequel, the last part of a television mini-series, the last installment of a literary series, or any final episode.