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

Results forwebdisk.popame.com

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2019-03-05T08:51:10.538	2019-03-05T07:51:09	2019-06-03T07:51:09	freejee.com	webdisk.popame.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-03-05T08:51:09.608	2019-03-05T07:51:09	2019-06-03T07:51:09	freejee.com	webdisk.popame.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-01-02T19:17:39.03	2019-01-02T18:17:38	2019-04-02T18:17:38	deenhub.com	webdisk.popame.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-01-02T19:17:38.508	2019-01-02T18:17:38	2019-04-02T18:17:38	deenhub.com	webdisk.popame.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2018-11-02T12:03:49.231	2018-11-02T11:03:48	2019-01-31T11:03:48	popame.com	webdisk.popame.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2018-11-02T12:03:48.675	2018-11-02T11:03:48	2019-01-31T11:03:48	popame.com	webdisk.popame.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3