A seed phrase (also called a recovery or mnemonic phrase) encodes all the private keys in your wallet into a human-readable list of words. If your device is lost, stolen, or damaged, the seed phrase lets you restore full access to your funds on a new wallet. Because it is the master key to everything, it must be recorded offline — ideally on paper or metal — and never typed into a website, photographed, or stored in the cloud. Losing it means losing your funds; exposing it means someone else can take them.