What it is: 12 words that act as a backup master key for your account.
What it's for: the only way back in if you forget your password — because we can't read your data, we can't reset it for you.
What it is NOT: it is not a password you type to log in, it is never emailed to you, and it is not stored or resettable by us.
Safety rule: anyone with these words controls your account and its wallet. Write them on paper, store them offline, and never share them.