A wildcard certificate can be used for your entire domain, including all subdomains. For example, you purchase the wildcard certificate *.eon.com.au. The ?*? means that you can use the certificate for any service on your domain domain name. You can then use this certificate on www.eon.net.au, mail.eon.net.au, vpn.eon.net.au?and so on.
Please be aware that some Wildcard certificates are not accepted by some servers. Please check with us before purchasing a wildcard certificate.