"Penultimate episode" refers to the second-to-last episode of a television series or the second-to-last part of a story. It comes right before the final episode or the conclusion of the story. Full definition
The fourth and penultimate episode of Telltale's Guardians of the Galaxy, Who Needs You, will release next week, and we have our first look of what we can expect from the inter-galactic travelers. (xboxenthusiast.com)
And after a wonderful penultimate episode last week, the finale was a bit too lackluster. (theyoungfolks.com)
Final Verdict: Amid the Ruins promises some interesting developments, but lacks the focus and central bad guy that made Season One's penultimate episode so thrilling. (oracleoffilm.com)