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.

Most early television series consisted of stand-alone episodes rather than continuing story arcs, so there was little reason to provide closure at the end of their runs. Early series that had special finale episodes include Howdy Doody in September 1960, Leave It to Beaver in June 1963, and in early 1964, Route 66.

Considered to be "the series finale that invented the modern-day series finale," the 1967 final episode of ABC's The Fugitive, "The Judgment: Part 2", attracted a 72% audience share when broadcast. This remained the highest viewership percentage in U.S. television history until the 1977 finale of the TV mini-series Roots (on the same network) and later the 1980 resolution episode of the internationally prominent "Who Shot J.R.?" cliffhanger of CBS' Dallas.

The most watched series finale in television history remains the 1983 finale of the CBS war/medical dramedy M*A*S*H, titled "Goodbye, Farewell and Amen". Viewed by 105.9 million viewers and drawing 77% of those watching televisions at the time, the finale of M*A*S*H held the record for most watched telecast of all-time for decades until 2010's Super Bowl XLIV edged it out with 106 million viewers, which coincidentally also aired on CBS. However, M*A*S*H's final episode remains the all-time most watched U.S. television episode (and so far, the only single television episode in U.S. history to be watched by at least 100 million viewers for a single telecast).

...
Wikipedia