What are recovery words (a seed phrase)?
A list of 12, 15, 18, 21 or 24 words that can restore wallet keys. Anyone who has them can take your bitcoin.
Not to be confused with: a passphrase — an extra word of your own that changes the walletPassphrase (25th word)An extra word or sentence added to recovery words, which creates a completely different wallet. Losing it means the words alone cannot help..
Many wallets follow BIP-39, which permits those five lengths. The words encode a random number from which the wallet's seed and derived keys are made. Write them down and keep them offline.
Never give them to a support agent, explorer or unsolicited website. Enter them only when you have deliberately chosen to restore your own wallet in trusted software, and check that the software is genuine first.
References
- Bitcoin Improvement Proposals, “BIP-39: Mnemonic code for generating deterministic keys”.