Wildcard SSL certificates are similar to SAN SSL certificates with some restrictions. With a wildcard certificate, you can secure multiple sub-domains with a single unique root domain. For example, if you have a wildcard certificate for www.yourdomain.com, it will also secure intranet.yourdomain.com and email.yourdomain.com with the same certificate. However, you will not be able to secure multiple unique domains such as, www.yourdomain.net and www.yourdomain.org. For additional information view the Symantec whitepaper Wildcard and SAN, Understanding Multiuse SSL Certificates.