Hierarchical Deterministic (HD) wallets generate private/public key pairs on-the-fly from a single root seed, usually represented as mnemonic words (BIP 39) or raw entropy. This seed spawns a branching tree of child keys—like m/44'/0'/0'/0/0 for standard addresses—enabling easy backups and organization of multiple accounts or coins. If you lose your device, you can re-import the seed in any compatible wallet, restoring every sub-account, address, and balance. HD wallets have become a mainstream practice, simplifying key management for both new and experienced users.