A public key is a key used in asymmetric cryptography, a cryptographic system that uses two different keys: a private key and a public key. The public key, as the name suggests, is made available to the public and is used for encryption or verifying digital signatures. It is derived from the private key, but unlike the private key, it cannot be used to derive the corresponding private key. The public key is used to encrypt data that can only be decrypted using the corresponding private key.
In summary, a public key is a part of a key pair used in asymmetric cryptography, primarily for encryption and verifying digital signatures. It is made public and can be freely shared, unlike the private key.