Wildcard SSL allows you to secure an unlimited number of subdomains on a single certificate. It’s a great solution for anyone who hosts or manages multiple sites or pages that exist on the same domain. The one-time cost of the certificate covers you for additional subdomains you may add in the future.
Unlike a standard SSL Certificate that is issued to a single Fully Qualified Domain Name only, e.g. www.yourdomain.com, which means it can only be used to secure the exact domain to which it has been issued, a Wildcard SSL Certificate is issued to *.yourdomain.com, where the asterisk represents all possible subdomains.
Wildcard SSL is an option available for DV and OV SSL Certificates.