A Certificate Authority (CA) is a body that verifies the identity of organisations or people. It does so by issuing a certificate to their “subjects”. A certificate contains the subject’s and the authority’s data as well as the subject’s public key and is digitally signed. A third party can rely on the certificate to identify the holder’s identity – provided he trusts the CA. See Wikipedia for more information. Unfortunately, not all CAs take the identification of their subjects seriously. Consequently, one should be cautious with the trust put into CAs.
Content Management System
A piece of software that allows to easily edit and publish a web-site. Traditionally these systems use a database and files to store the contents of the web-page. Also, such a system traditionally provides a web front-end that allows editing the page’s content in a web browser. There is a variety of such systems available, both as open and closed source. See Wikipedia for more information.
Public Key Infrastructure
A system of keys enabling encrypted communications, which allows identification of the interlocutors even without them not knowing each other. It is based on private and public keys for asymmetric encryption. On top Certificate Authorities (CA) verify the identity of a communication partner by issuing a certificate to this person. If you trust the CA, you can rely on the authenticity of the person holing a certificate issued by it. Communication encrypted with modern keys can be considered private, regardless of the trust put into the CA. See Wikipedia for a more detailed description.