Wildcard SSL certificates are used for securing multiple sub-domains of a certain website. Every sub-domain should be part of the sames domain.
Examples:
Every company can benefit from using the convenient Wildcard SSL certificate. It·s main advantage is that it could consolidate every certificate your company is using into a single SSL cert. Additionally, the Wildcard SSL will optimize your budget by decreasing the number of used SSLs and lowering their maintenance time.
This type of certificate comes with unlimited server license.