What is a Wildcard SSL Certificate?

A Wildcard SSL Certificate can be used for unlimited first-level sub-domains of the domain name you specify in your Certificate Signing Request (CSR). For example, if you hosted www.domain.com, a Wildcard SSL Certificate for *.domain.com would allow you to secure

www.domain.com
mail.domain.com
admin.domain.com
sales.domain.com
europe.domain.com
anything.domain.com

The * character in the common name is the wildcard character. It can take on any first-level subdomain name.