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

Results forcpcalendars.predatorbuilder.com

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2020-09-13T17:23:27.899	2020-09-13T16:23:27	2020-12-12T16:23:27	predatorbuilder.writersharbor.org	cpcalendars.predatorbuilder.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-09-13T17:23:27.441	2020-09-13T16:23:27	2020-12-12T16:23:27	predatorbuilder.writersharbor.org	cpcalendars.predatorbuilder.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-07-13T16:41:03.768	2020-07-13T15:41:03	2020-10-11T15:41:03	autodiscover.harborwriters.com	cpcalendars.predatorbuilder.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-07-13T16:41:03.352	2020-07-13T15:41:03	2020-10-11T15:41:03	autodiscover.harborwriters.com	cpcalendars.predatorbuilder.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-05-12T16:38:44.556	2020-05-12T15:38:44	2020-08-10T15:38:44	cpcalendars.predatorbuilder.com	cpcalendars.predatorbuilder.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-05-12T16:38:44.241	2020-05-12T15:38:44	2020-08-10T15:38:44	cpcalendars.predatorbuilder.com	cpcalendars.predatorbuilder.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3