A hardware wallet is a digital device whose sole purpose is to generate and store public and private keys and sign transactions. Hardware wallets allow users to send and receive Bitcoin in a secure fashion. Hardware wallets are a form of cold storage, meaning that they allow a user to keep their private keys safely disconnected from the internet.
Most hardware wallets implement BIP 32 and BIP 39 standards, meaning they use Hierarchical Deterministic wallets and mnemonic phrases. Like all wallets, different hardware wallets vary in terms of security, privacy, and reliability.