Definition: Certificates are electronic attachments issue by a CA (Authorities) that are used to facilitate authentication and information assurance. The verification data issued by a CA is based upon the public key infrastructure. The record or document is normally referred to as a digital signature and it is frequently based on an established protocol known as X.509. The protocol supports the SSL (or Secure Socket Layer). The receiver of a message can verify the identity of the sender and in turn encrypt and send a response back to the sender. There are a number of CAs that are well known, such as VeriSign and Entrust.
Its Relevance: The public key infrastructure is essential to the free flow of electronic commerce. You must utilize one form of encrypted and authenticated communication methods to be able to competitive and safely operate in an on-line environment.