A season finale is the last episode of a television SERIES in a given season. It is usually the most important episode of the season, as it often contains a major plot twist or cliffhanger that sets up the next season. The term 'season finale' can also refer to the last episode of a SERIES, if the show is not renewed for another season. In this case, the answer to the crossword puzzle is SERIES, which is a six-letter word.