SSL certificate can be organized into two types: validation level and secured domains.
Certificates can be issued for multiple domains and even wildcard domains. But because of the extended validation specification, these certificates can only be issued for a single domain, not multiple or wildcard domains. This is because of the sensitivity of the verification process.
There are a couple of different types of SSL certificates based on the method that you choose to confirm your identity. The three levels increase in complexity and vary in the type of information requested to validate the certificate.