There are three different types of SSL certificates: Domain Validated (DV), Organization Validated (OV), and Extended Validation (EV). All of these certificates encrypt, but the main difference is in how much trust they add to a website. DV certificates can be issued in mere minutes, with the Certificate Authority (CA) just needing to validate that the customer owns the domain they wish to secure. Both OV and EV certificates require a more thorough vetting, but these certificates enable a number of different trust icons within a browser and on a website to ensure online visitors that it is safe to make purchases and/or share information. The most important and recognized trust indicator is the green address bar, which only comes with EV SSL certificates.
A standard DV, OV, and EV certificate can protect one domain (both www and non-www if the certificate is generated as a “www.domain.com”). However, there are multi-domain certificates available which can secure multiple domains on just a single cert, as their name suggests. Depending on the brand of the certificate, a multi-domain solution can secure up to 101 total domains.
There are also Wildcard SSL certificates available. These certificates secure one main domain (www.domain.com)along with an unlimited amount of subdomains (mail.domain.com, etc.domain.com, subdomain.domain.com, etc.).