The term Public-key cryptography is often referred as asymmetric cryptography, a class of cryptographic protocols based on algorithm that require two separate keys. In general, it is a cryptographic system that implements two keys- a public key, which is known to everyone and a private key or secret key, which is known only to the recipient of the message. The public key is used to encrypt the plain text, while the private key is used for reverse operation, to decrypt the cypher text.
A vital element to the public key system is that the public keys are related in a manner that only the public key can be used to encrypt the text and only the corresponding secret key can be used to decrypt that message. In addition to this, it is virtually impossible to deduce the private key if you already aware about the public key. Public-key systems, for example Pretty Good Privacy (PGP), are becoming widely popular for transmitting information through internet.