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

Results forsitemaps.crowdreference.com

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2021-06-04T04:43:43.705	2021-06-04T03:43:43	2021-09-02T03:43:43	sitemaps.crowdreference.com	sitemaps.crowdreference.com	C=US, O=Let's Encrypt, CN=R3
2021-06-04T04:43:43.479	2021-06-04T03:43:43	2021-09-02T03:43:43	sitemaps.crowdreference.com	sitemaps.crowdreference.com	C=US, O=Let's Encrypt, CN=R3
2021-03-09T15:15:38.663	2021-03-09T14:15:38	2021-06-07T14:15:38	sitemaps.crowdreference.com	sitemaps.crowdreference.com	C=US, O=Let's Encrypt, CN=R3
2021-03-09T15:15:38.443	2021-03-09T14:15:38	2021-06-07T14:15:38	sitemaps.crowdreference.com	sitemaps.crowdreference.com	C=US, O=Let's Encrypt, CN=R3
2020-12-15T18:14:28.944	2020-12-15T17:14:28	2021-03-15T17:14:28	sitemaps.crowdreference.com	sitemaps.crowdreference.com	C=US, O=Let's Encrypt, CN=R3
2020-12-15T18:14:28.651	2020-12-15T17:14:28	2021-03-15T17:14:28	sitemaps.crowdreference.com	sitemaps.crowdreference.com	C=US, O=Let's Encrypt, CN=R3