SSL (Secure Sockets Layer) is the standard security technology for establishing an encrypted link between a web server and a browser. This link ensures that all data passed between the web server and browsers remain private and integral.
Secures a single Fully Qualified Domain Name such as www.yourdomain.com or secure.yourdomain.com
Secures all sub-domains on a single Fully Qualified Domain Name. e.g. the Certificate is issued to *.yourdomain.com