You're walking somewhere you've never been before and suddenly feel as though you've strolled down the same road already. You're experiencing the well-known phenomenon déjà vu — but what is déjà vu, really, and why does the strange feeling happen?
Déjà vu is a French expression meaning "already seen," which was first used in 1876 by French philosopher Émile Boirac in a letter to his book editor, and later in his published book "The Psychology of the Future" (Keagan Paul, 1918).
