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

Results forqa2.api.kater.com

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2020-01-04T09:19:48.602	2019-08-27T00:00:00	2020-09-27T12:00:00	api.kater.com	*.api.kater.com	C=US, O=Amazon, OU=Server CA 1B, CN=Amazon
2019-09-26T19:05:07.974	2019-09-26T18:05:07	2019-12-25T18:05:07	qa2.api.kater.com	qa2.api.kater.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-09-26T19:05:07.046	2019-09-26T18:05:07	2019-12-25T18:05:07	qa2.api.kater.com	qa2.api.kater.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-08-27T17:04:21.718	2019-08-27T00:00:00	2020-09-27T12:00:00	api.kater.com	*.api.kater.com	C=US, O=Amazon, OU=Server CA 1B, CN=Amazon
2019-07-04T23:28:22.971	2019-07-04T22:28:22	2019-10-02T22:28:22	qa2.api.kater.com	qa2.api.kater.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-07-04T23:28:22.591	2019-07-04T22:28:22	2019-10-02T22:28:22	qa2.api.kater.com	qa2.api.kater.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3