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

Results forwebdisk.pullcustomers.com

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2019-01-02T10:58:30.389	2019-01-02T09:58:29	2019-04-02T09:58:29	pullcustomers.com	webdisk.pullcustomers.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-01-02T10:58:29.478	2019-01-02T09:58:29	2019-04-02T09:58:29	pullcustomers.com	webdisk.pullcustomers.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2018-11-02T07:56:33.927	2018-11-02T06:56:33	2019-01-31T06:56:33	pullcustomers.com	webdisk.pullcustomers.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2018-11-02T07:56:33.287	2018-11-02T06:56:33	2019-01-31T06:56:33	pullcustomers.com	webdisk.pullcustomers.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3