It can be anything! An apex, subdomain, or even a URL.

Results for*.test.castingnetworks.com

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2018-01-16T16:01:15.546	2017-02-10T00:00:00	2018-03-10T12:00:00	*.test.castingnetworks.com	*.test.castingnetworks.com	C=US, O=Amazon, OU=Server CA 1B, CN=Amazon
2018-01-16T16:01:15.546	2017-02-10T00:00:00	2018-03-10T12:00:00	*.test.castingnetworks.com	*.test.castingnetworks.com	C=US, O=Amazon, OU=Server CA 1B, CN=Amazon
2017-05-22T18:20:03.111	2017-03-23T00:00:00	2018-04-23T12:00:00	*.test.castingnetworks.com	*.test.castingnetworks.com	C=US, O=Amazon, OU=Server CA 1B, CN=Amazon
2017-05-22T18:20:03.111	2017-03-23T00:00:00	2018-04-23T12:00:00	*.test.castingnetworks.com	*.test.castingnetworks.com	C=US, O=Amazon, OU=Server CA 1B, CN=Amazon