A public key is a unique alphanumeric code, generated randomly as part of a cryptographic key pair. It is openly shared and functions as an address or identifier for receiving funds or encrypted messages. The public key is formed from its corresponding private key using a complicated math procedure. Even though the public key is used to encrypt data and validate digital signatures, it cannot be reversed or decoded to reveal the private key. Public keys play a critical role in securing transactions and establishing trust within cryptographic systems.