A public key is a cryptographic key that is used in asymmetric encryption. It allows users to encrypt messages or data that can only be decrypted by a corresponding private key. This system ensures that only the intended recipient, who possesses the private key, can read the information. Public keys are widely used in various applications, such as securing online communications and digital signatures. They are part of a larger framework known as public key infrastructure (PKI), which helps manage keys and certificates, ensuring secure transactions over the internet.