You've probably opened multiple accounts successfully through Metamask and sometimes secured a securely entered private key and sometimes a passphrase and this way I want to compare the above two important items. While the recovery passphrase is used to create and recover your entire MetaMask wallet that you opened with a specific passphrase and you may have noticed that you enter the passphrase and a different address is displayed because the passphrase includes all accounts (addresses) created in that wallet , Each account(address) has its own private key. This key can be used to import that account (address), and only that account, into another wallet.