A public key is the public half of the public/private keypair. Anyone can use a public key check that a signature is correct, but they can't generate the signature themselves with the public key.
A public key is the public half of a public/private ECDSA keypair. It is meant to be shared and without revealing the private key. Public keys can be used to verify a digital signature and encrypt data that can only be decrypted by the private key.