A hierarchical deterministic wallet, or HD wallet, is a type of cryptocurrency wallet that uses a system of keys to generate a large number of private and public keys from a single seed key. This is known as deterministic key generation, and it allows the wallet to be easily backed up and restored. An HD wallet also has a hierarchical structure, which means that the keys are organized into different levels or "chains" of keys. This allows the wallet to support multiple accounts and addresses, and it makes it easier to manage and organize the keys. HD wallets are commonly used for Bitcoin and other cryptocurrencies, and they are considered to be more secure and user-friendly than non-deterministic wallets. It is an industry standard described in BIP32 and BIP44.