What is a seed phrase?

A seed phrase is the written backup for your bitcoin. It is usually 12 or 24 ordinary words, in order. With those words you can open the same wallet again on a new phone or device.

A wallet here means the app or hardware device that holds your private cryptographic keys. It does not hold the coins themselves.

A private cryptographic key (often shortened to private key) is a number that proves you can spend bitcoin. Your seed phrase rebuilds every private cryptographic key your wallet needs. Lose the words, or let someone else copy them, and that spending power goes with them.

Twelve or twenty-four ordinary words

When you create a new wallet, it shows a list of 12 or 24 words. Write them down by hand, in the same order.

Those words come from a fixed list defined by BIP 39. BIP means Bitcoin Improvement Proposal: a numbered community standard that wallets follow. BIP 39 is the name of this word-list standard (it also allows 15, 18, or 21). The words look ordinary on purpose — everyday dictionary words — so you can write them and check them later.

Order matters. Change the order and you get a different wallet.

One phrase rebuilds every key

Every place your wallet can receive bitcoin — and new ones it makes later — all come from that same phrase. You do not get a new seed for each payment.

That is why the seed matters more than any one phone or device. If the device dies, you enter the same words into a wallet that follows the same rules, and you get the same private cryptographic keys back.

Some people also set an optional extra password some wallets call a passphrase, on top of the seed. If you set one, you need the seed and that passphrase to rebuild the same wallet. There is no reset if the passphrase is forgotten. Skip this for now if you are just learning; the backup guide covers it later. See also Where is my bitcoin, really?.

The wallet holds keys, not coins

Bitcoin’s balances live on a shared public record (often called the blockchain), not inside your wallet. Your wallet holds the private cryptographic keys that prove a spend is yours. The seed phrase is the short backup of those keys.

On an exchange (a company that holds bitcoin for customers), the company holds the private cryptographic keys. You hold a promise to be paid. When you hold your own keys — often called self-custody — you hold the spending power yourself. The seed is how you keep that if a phone dies or a device is replaced. More on that trade-off: Why self-custody matters.

What never to do with the words

Never photograph, screenshot, type, email, save in the cloud, or print your seed. Never enter it on a website, phone keyboard, or computer to “check” it. A photo in your camera roll, a note that syncs online, a print job sitting on a printer, or a fake “support” form is how seeds get stolen.

• Write by hand on the card the device gives you (pencil or archival ink).
• Confirm on the device screen when the wallet asks you to check words — not by typing them into a laptop.
• Treat anyone who asks for your words as a thief. Real support never needs your seed.

If someone else has the words

Whoever has the seed (and the optional extra password some wallets call a passphrase, if you set one) can spend from anywhere. There is no bank freeze and no chargeback. That is the same power that lets you recover after a lost device.

What to do next

1. Learn how to back the phrase up so it survives fire, flood, and time: Seed phrase backup.
2. If you want a device that creates and protects private cryptographic keys offline, start here: Choosing a hardware wallet.
3. Curious about 12 vs 24 words and the optional extra password some wallets call a passphrase? See the seed phrase math.

Common mistakes

• Thinking the coins sit inside the wallet — the wallet holds private cryptographic keys; the public record holds the balances.
• Saving a “temporary” photo or cloud note “just until metal arrives.”
• Skipping the backup guide and leaving only a paper card in a drawer forever.
• Sharing the words with a helper, remote tech, or “recovery service.”