HD wallet stands for Hierarchical Deterministic wallet. These wallets are introduced by BIP32 and later by BIP44. HD wallet is a wallet structure that contains private keys that are derived from a single seed. A single seed is used to create a master private key. From which private keys are derived in a tree structure.
A master private key is used to derive parent keys, which can derive child keys. Each child key can derive grandchild keys and so on. A single seed (recovery phrases) is enough to backup and recover all the derived keys. Also you can import and export your seed to another wallet.
Since your addresses are derived from your private keys HD wallets can generate an infinite amount of addresses every time a crypto transaction is made. Nowadays most wallets are HD wallets and these wallets generate 12-24 seed phrases which you can use to recover your wallet.