A Wildcard SSL is the ‘unlimited sub domain’ version of a single SSL. If you purchase a single SSL, then it only supports one version of your domain name, e.g. secure.itomic.com.au, or admin.itomic.com.au, or www.itomic.com.au, or uat.itomic.com.au. If you buy a Wildcard SSL, then all the previous examples would be covered by the same SSL certificate, in other words *.itomic.com.au. Itomic strongly prefers and recommends a Wildcard SSL for all websites.