(covers information from several alternate timelines)
An episode was a single installment of a television series.
As of 1996, Rain Robinson had seen every episode of Mission: Impossible. (VOY: "Future's End")
In 2152, Trip Tucker remarked that T'Pol's story of Vulcans making unofficial first contact with Humans in 1957, which he summarized as "Two Vulcans stroll into a bar, hustle a few games of pool and walk out with an armload of TV dinners." sounded like an episode of The Twilight Zone. (ENT: "Carbon Creek")
In 2263 of the alternate reality, James T. Kirk remarked in his captain's log that the USS Enterprise's missions were beginning to feel episodic to him. (Star Trek Beyond)
This was a tongue-in-cheek reference to Star Trek: The Original Series, whose episodes were mostly written as standalone entries, rather than forming part of a larger story arc.
In 2376, B'Elanna Torres located an episode of The Untouchables in which Eliot Ness captured Al Capone. (VOY: "Memorial")