Seed phrase
Also: recovery phrase, secret recovery phrase, seed
A seed phrase, or recovery phrase, is a list of usually 12 or 24 words that a wallet shows you when you create it. All of the wallet's private keys and addresses, across networks, are derived from those words. If you lose your phone, the phrase restores the wallet on another device.
It also means the seed phrase is full access to your money. Nobody honest will ever ask for it: not wallet support, not an exchange, not a group admin, not an airdrop site. The most popular scams are about extracting the phrase through fake tech support, fake wallet apps or “wallet verification” sites. Write the phrase down offline, on paper or metal, and keep it somewhere safe.