A paper wallet is the Secret Key by itself, most often written or printed on paper and sometimes with QR codes for easy transfer.

Although the Public Key and Address can be derived from the secret key alone, a paper wallet will often have the address printed with it so that more funds can be sent to that address.

A paper wallet should only be used if it was securely generated. Paper wallets must be kept safe, as elsewhere discussed a piece of paper can be destroyed in many ways.