Single Domain SSL - covers a single domain name with a "www" hostname. Ex: test.com & www.test.com
Wildcard SSL - covers a single domain name with its subdomains. Ex: test.com & *.test.com
Multi-Domain SSL - covers multiple domain names. A single domain and its www hostname count as different domains in this category. Ex: test.com, www.test.com, abc.com, etc.
SSL certificate validation level:
* Domain Validation (DV SSL) Certificates - It has the lowest level of validation. For example, CAs do not check the person's identity who runs a website.
* Organization Validated (OV SSL) Certificates - The process of identity checking is high from DV SSL. CAs verify the identity of the business that owns the domain name.
* Extended Validated (EV SSL) Certificates - You will get the highest level l of validation. CAs verify the domain organization, physical location, legal existence, ownership, etc.