Seed phrase
A list of words, usually 12 or 24, that backs up a wallet and can restore all of its keys.
A seed phrase is a list of words, usually 12 or 24, that backs up a wallet and can restore all of its keys. Lose your phone, drop your hardware wallet in the sea, factory-reset by accident: type the words into a new wallet and every key comes back, with the balances intact.
The words are not random scribbles. They follow a standard called BIP-39, which uses a fixed list of 2,048 words. Each word maps to a number, and together those numbers encode the master secret your wallet grows every private key from. Two wallets fed the same phrase rebuild the same keys.
That power cuts both ways. The phrase is the wallet. Anyone who reads your 12 or 24 words can recreate your keys on their own device and drain the funds, with no need for your physical hardware. So the backup that saves you is also the single thing a thief wants most.
Write it on paper, or stamp it into metal if you want it to survive a fire. Then store it offline. Never photograph it, never type it into a website, never paste it into cloud notes or email. The common scam is a fake wallet popup or support agent asking you to confirm your phrase. Real wallets never ask.
The danger is not only theft. Stefan Thomas lost access to 7,002 BTC because he forgot the password guarding his keys and had no usable backup. A seed phrase exists to prevent exactly that, but only if you can find it and read it years later.
One phrase often controls many addresses across several coins. Back it up once, properly, and you protect the lot. This is the backbone of self-custody: the words are yours, and so is the job of guarding them.