GNU Privacy Guard, better known as GnuPG or just GPG, is an implementation of public key cryptography. This allows you to securely transmit information between parties that can be used to ensure the information is genuine and only accessible by authorized parties.
GPG relies on the OpenPGP standard (RFC-4880), an open-source implementation of Phil Zimmermann's work with Pretty Good Privacy (PGP). GPG can provide digital encryption, signing, and key exchange and is interoperable with modern versions of PGP.