Wildcard SSL Certificates are completely different from single domain certificate as it is issued to domain name with asterisk sign (*). *.yourdomain.co. This * stands for wildcard ssl. With single Wildcard SSL you can secure all your sub domains (abc.yourdomain.com, 123.yourdomain.com, admin.yourdomain.com and more) in single ssl certificate.
With RapidSSL Wildcard, you can install single wildcard ssl certificate on unlimited server licenses and unlimited sub domains. RapidSSL wildcard certificate is highly trusted and wildly used wildcard ssl solution for those needs securing number of sub domains for less.