SSL stands for Secure Socket Layer and is noticed when you visit a website that begins with https://. The "s" in https:// means the site is secure - that is, the connection between your computer and the website server is encrypted.

With SSL certificates you can start conducting secure online transactions with confidence, quickly and cost-effectively. All of our SSL certificates enable up to 256-bit encryption and can be used to secure servers used for Web sites, intranets, extranets and other online applications.

An SSL Certificate can be thought of as a digital piece of paper that states who the SSL connection is being made with and some kind of "Certificate Authority (CA)," which is a third party that verifies the certificate information is accurate.

SSL Certificates can be self-signed or signed by a CA. If you self-sign a certificate, it will not be trusted by any web browsers or other SSL clients. That is because the entity who generated the certificate signed it themselves and basically said "this information is accurate, trust us!" This will result in a warning in your web browser or SSL client, but the SSL connection will still be created and will still be encrypted. For all intensive purposes, a self-signed certificate is just as good for encryption as a CA-signed one. 

A certificate that is signed by a CA is usually trusted by most, if not all, web browsers and SSL clients. This is because the SSL clients are preprogrammed to accept certificates provided by entities who have proven their trust (such as Verisign, Thawte, and GeoTrust, the top three CAs). Certificates provided by these CAs will not result in a warning in your web browser or SSL client and looks more professional.

The certificates are also verified against the domain and company the certificate was issued to. Therefore, if the SSL certificate of the new website you're trying to purchase a book from was issued by Verisign, you can feel confident that the company does exist and the domain belongs to that company.