A wildcard SSL certificate secures your website URL and an unlimited number of its subdomains with a single SSL Certificate.
A single wildcard certificate can secure both www.yourcompany.com and blog.yourcompany.com.
Using the wildcard notation (an asterisk and period before your domain name) allows you to extend security to different subdomains based on the level you specify in your request.
If you configure *.yourcompany.com, you can secure
If you configure *.www.yourcompany.com, you can secure
Some web servers might require a unique IP address for each subdomain on the Wildcard certificate.
NOTE: Wildcard certificates only secures the level of subdomain you specify. So, if a certificate is configured for *.www.yourcompany.com, it will not secure www.yourcompany.com. Check with your Certificate Authority for details.