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

Results fortestcdn.compadata.com

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2020-07-14T10:28:53.769	2020-07-14T09:28:53	2020-10-12T09:28:53	testcdn.compadata.com	testcdn.compadata.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-07-14T10:28:53.452	2020-07-14T09:28:53	2020-10-12T09:28:53	testcdn.compadata.com	testcdn.compadata.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-07-14T09:59:40.325	2020-07-14T08:59:40	2020-10-12T08:59:40	testcdn.compadata.com	testcdn.compadata.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-07-14T09:59:40.183	2020-07-14T08:59:40	2020-10-12T08:59:40	testcdn.compadata.com	testcdn.compadata.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-07-14T09:58:03.393	2020-07-14T08:58:03	2020-10-12T08:58:03	testcdn.compadata.com	testcdn.compadata.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-07-14T09:58:03.141	2020-07-14T08:58:03	2020-10-12T08:58:03	testcdn.compadata.com	testcdn.compadata.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3