Private key
A secret number that proves ownership of Bitcoin and authorizes transactions. Whoever holds the private key controls the funds.
Seed phrase
Definition
A seed phrase (also called a recovery phrase or mnemonic) is generated when you first create a wallet. Writing it down on paper and keeping it somewhere safe is the most important step in protecting your bitcoin, because anyone with these words can restore the wallet and access the funds.
Example
If your phone breaks, entering your seed phrase into a new wallet restores all your Bitcoin.