A wildcard certificate protects unlimited subdomains of a domain.

A wildcard certificate protects unlimited subdomains of a domain. (e.g. shop.checkdomain.de, mail.checkdomain.de, etc.).

The advantage of an SSL certificate is that one obtains a certificate for all subdomains used and does not have to apply for each subdomain specifically an SSL certificate.

Please note that a wildcard certificate is only valid for one level. So as mentioned above e.g. for shop.checkdomain.de, but not for de.shop.checkdomain.de. If one would like to protect this level, one would have to apply for another Wildcard certificate for this level.

With SSL Wildcard Certificates, a separate IP address is required for each independent website. Meanwhile there are other solutions depending upon Apache version however also e.g. IP Sharing.