A tense was a form of a verb that indicated the time something had, is, or would happen. The tense that described actions that have happened is called past tense.
In the 29th century, when discussing the placement of a temporal disruptor on USS Voyager with Seven of Nine, frequent time traveler Captain Braxton noted that "I gave up trying to keep my tenses straight years ago.". (VOY: "Relativity")