Certificates differ in how many names they cover.
SINGLE DOMAIN
Covers one hostname, and conventionally both the bare domain and its www form. yourdomain.com and www.yourdomain.com.
Does not cover subdomains such as shop.yourdomain.com.
WILDCARD
Covers a domain and all its first-level subdomains: *.yourdomain.com covers shop, blog, mail and anything else at that level.
Does not cover second-level subdomains such as test.shop.yourdomain.com, and wildcards require DNS-based validation.
MULTI-DOMAIN
Sometimes called SAN or UCC certificates. Covers a specified list of different domains on one certificate.
Useful where one server hosts several unrelated domains and you want a single certificate to manage.
WHAT AUTOSSL DOES
AutoSSL issues certificates covering each domain and its existing subdomains automatically, adding new ones as they are created. For most accounts this removes the need to think about certificate types at all.
WHEN YOU NEED A WILDCARD
If you create subdomains frequently and programmatically, so AutoSSL cannot keep up. Otherwise AutoSSL's per-subdomain approach is simpler.
