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

Results forlogin.staging.adloop.co

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2020-07-08T02:02:08.923	2020-07-08T01:02:08	2020-10-06T01:02:08	login.staging.adloop.co	login.staging.adloop.co	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-07-08T02:02:08.233	2020-07-08T01:02:08	2020-10-06T01:02:08	login.staging.adloop.co	login.staging.adloop.co	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-05-08T18:55:21.186	2020-05-08T17:55:20	2020-08-06T17:55:20	login.staging.adloop.co	login.staging.adloop.co	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-05-08T18:55:20.994	2020-05-08T17:55:20	2020-08-06T17:55:20	login.staging.adloop.co	login.staging.adloop.co	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-03-09T17:50:50.76	2020-03-09T16:50:49	2020-06-07T16:50:49	login.staging.adloop.co	login.staging.adloop.co	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-03-09T17:50:50.511	2020-03-09T16:50:49	2020-06-07T16:50:49	login.staging.adloop.co	login.staging.adloop.co	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3