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

Results forstaging.crowdreference.com

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2021-06-22T22:58:49.31	2021-06-22T21:58:49	2021-09-20T21:58:48	staging.crowdreference.com	staging.crowdreference.com	C=US, O=Let's Encrypt, CN=R3
2021-06-22T22:58:49.164	2021-06-22T21:58:49	2021-09-20T21:58:48	staging.crowdreference.com	staging.crowdreference.com	C=US, O=Let's Encrypt, CN=R3
2021-03-27T06:29:26.069	2021-03-27T05:29:25	2021-06-25T05:29:25	staging.crowdreference.com	staging.crowdreference.com	C=US, O=Let's Encrypt, CN=R3
2021-03-27T06:29:25.822	2021-03-27T05:29:25	2021-06-25T05:29:25	staging.crowdreference.com	staging.crowdreference.com	C=US, O=Let's Encrypt, CN=R3