A wallet that requires multiple independent private keys to jointly approve any transaction — a 3-of-5 setup means at least three out of five keys must agree before a transaction goes through, so a single compromised, lost, or rogue holder can't move funds alone. But this protection only covers the signing authority itself, not whether the content each signer actually sees and verifies has been tampered with.

A sequence of 12 or 24 words that serves as the root from which all of a wallet's private keys are derived — whoever holds it holds everything in the wallet, and no password or 2FA can stand behind it.