déjà vu = seen before
déjà entendu = heard before
jamais vu = never seen - is the phenomenon of experiencing a situation that one recognises but that nonetheless seems very unfamiliar
A report published in Current Directions in Psychological Science states that déjà vu occurs when a current situation resembles a situation that has previously occurred in one’s life. When multiple elements of the two situations overlap, the feeling of familiarity is sparked.
"There is another experience worth mentioning; jamais vu. Its the opposite of deja vu. Instead of feeling extra familiar, thing seem totally unfamiliar. In this case there is too little connection between long-term memory and perceptions from the present. When a person is in this state, nothing they experience seems to have anything to do with the past. They might be talking to a person they know well and suddenly they person seems totally unfamiliar. Their sense of knowing the person, and knowing how to relate to them simply vanishes. A room in which they spend a lot of time suddenly becomes totally novel; everything seems new. Details they will have seen a thousand times suddenly become engaging."
--from "Deja Vu in Spiritual and Scientific Views,"