Answer Description
Subject Alternative Name Certificates are public certificates with a list of alternative domains, sub domains and/or IP addresses that can also use the certificate. For example CrucialExams.com, www.CrucialExams.com, api.CrucialExams.com and the IP 4.5.4.5 all in a single cert. Wildcards are a close alternative that supports any sub domain (e.g. *.google.com) but a wildcard could not also be used for gmail.com. To use a single certificate for a sub-domain and entirely different domain a SAN must be used.