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

Results forcom.rhubab.com

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2021-08-15T11:45:36.151	2021-08-15T10:45:35	2021-11-13T10:45:33	radiator.cc	www.zincmax.com.rhubab.com	C=US, O=Let's Encrypt, CN=R3
2021-08-15T11:45:36.012	2021-08-15T10:45:35	2021-11-13T10:45:33	radiator.cc	www.zincmax.com.rhubab.com	C=US, O=Let's Encrypt, CN=R3
2021-04-20T06:04:29.951	2021-04-20T05:04:29	2021-07-19T05:04:29	comisionhero.com.rhubab.com	comisionhero.com.rhubab.com	C=US, O=Let's Encrypt, CN=R3
2021-04-20T06:04:29.831	2021-04-20T05:04:29	2021-07-19T05:04:29	comisionhero.com.rhubab.com	comisionhero.com.rhubab.com	C=US, O=Let's Encrypt, CN=R3