Déjà vu was a Terran term (from the French language for "already seen") used to describe the feeling of having previously experienced something that was being experienced for the first time. (ENT: "Future Tense") The corresponding term in Klingonese was "nIb'poH." (TNG: "Cause and Effect")
Tuvok referred to the phenomenon as "paradoxical state-dependent associative phenomenon." In 2373, Lieutenant Commander Tuvok said that Ensign Harry Kim was experiencing it when he claimed that the USS Voyager had visited the star system before where the Taresian homeworld is located. (VOY: "Favorite Son")