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

Results forwebdisk.upsilon.vc

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2019-03-17T07:06:19.378	2019-03-17T06:06:18	2019-06-15T06:06:18	upsilon.vc	webdisk.upsilon.vc	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-03-17T07:06:18.829	2019-03-17T06:06:18	2019-06-15T06:06:18	upsilon.vc	webdisk.upsilon.vc	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2018-05-01T04:13:30.785	2018-05-01T00:00:00	2018-07-30T23:59:59	upsilon.vc	webdisk.upsilon.vc	C=US, ST=TX, L=Houston, O="cPanel, Inc.", CN="cPanel, Inc. Certification Authority"
2018-05-01T04:13:10.121	2018-05-01T00:00:00	2018-07-30T23:59:59	upsilon.vc	webdisk.upsilon.vc	C=US, ST=TX, L=Houston, O="cPanel, Inc.", CN="cPanel, Inc. Certification Authority"