While wallets are often described as being a place to hold or store bitcoins,[36] due to the nature of the system, bitcoins are inseparable from the block chain transaction ledger. Perhaps a better way to define a wallet is something "that stores the digital credentials for your bitcoin holdings"[37] and allows you to access (and spend) them. Bitcoin uses public-key cryptography, in which two cryptographic keys, one public and one private, are generated.[38] The public key can be thought of as an account number or name and the private key, ownership credentials. At its most basic, a wallet is a collection of these keys. Most bitcoin software also includes the ability to make transactions, however.
Perhaps better termed physical wallets, physical bitcoins are ubiquitous in media coverage and combine a novelty coin with a private key printed on paper, metal,[39] wood,[40] or plastic. Physical bitcoins aren't widely seen outside of pictures in news article[citation needed], but for those serious about security, storing private keys on paper printouts or in offline data storage devices is the best option.[37