Déjà vu (French for "already seen") is the unsettling feeling that you've lived through the current moment, person, or place before that you've experienced a new situation before, even though you also know rationally that the feeling is false, and realize it's impossible. It's a brief, startling sensation that often lasts only seconds, and it's usually described as a memory glitch in which your brain mistakenly tags a fresh event as familiar. It's a common, harmless phenomenon, especially among young people, possibly caused by slight memory errors, brain circuit hiccups, or similarities between a new place and a forgotten memory.