Some believe déjà vu is the memory of dreams. The reasoning goes like this: though the majority of dreams are never remembered, a dreaming person can display activity in the areas of the brain that process long-term memory. Perhaps a dream can read directly into long-term memory, bypassing short-term memory entirely. In this case, déjà vu might be a memory of a forgotten dream with elements in common with the current "awake" experience. This may be similar to another phenomenon known as deja rêvé, or "already dreamed."

Jamais vu: From the French, meaning "never seen," the expression means explicitly not remembering having seen something before. The person knows it has happened before, but the experience feels unfamiliar. Often described as the opposite of déjà vu, jamais vu involves a sense of eeriness and the observer's impression of seeing the situation for the first time, despite rationally knowing that he or she has been in the situation before. Jamais vu is sometimes associated with certain types of amnesia and epilepsy. An old internet joke referred to this feeling as "vujà dé."
Presque vu: From the French language, meaning "almost seen," the expression means almost, but not quite, remembering something. Often very disorienting and distracting, presque vu rarely leads to an actual breakthrough. Frequently, one experiencing presque vu will say that they have something "on the tip of their tongue". Presque vu is often cited by people who suffer from epilepsy or other seizure-related brain conditions, such as temporal lobe lability.
Déjà éprouvé: "already attempted or tried"