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

Results forfront-end.hunterdevbox.com

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2021-08-05T01:59:20.129	2021-08-05T00:59:19	2021-11-03T00:59:17	back-end.hunterdevbox.com	front-end.hunterdevbox.com	C=US, O=Let's Encrypt, CN=R3
2021-08-05T01:59:19.944	2021-08-05T00:59:19	2021-11-03T00:59:17	back-end.hunterdevbox.com	front-end.hunterdevbox.com	C=US, O=Let's Encrypt, CN=R3
2021-08-04T18:43:57.968	2021-08-04T17:43:57	2021-11-02T17:43:55	back-end.hunterdevbox.com	front-end.hunterdevbox.com	C=US, O=Let's Encrypt, CN=R3
2021-08-04T18:43:57.832	2021-08-04T17:43:57	2021-11-02T17:43:55	back-end.hunterdevbox.com	front-end.hunterdevbox.com	C=US, O=Let's Encrypt, CN=R3