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

Results fordan.customizablewatch.com

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2021-03-07T04:09:44.408	2021-03-07T03:09:43	2021-06-05T03:09:43	dan.customizablewatch.com	dan.customizablewatch.com	C=US, O=Let's Encrypt, CN=R3
2021-03-07T04:09:44	2021-03-07T03:09:43	2021-06-05T03:09:43	dan.customizablewatch.com	dan.customizablewatch.com	C=US, O=Let's Encrypt, CN=R3
2020-12-14T04:07:36.565	2020-12-14T03:07:36	2021-03-14T03:07:36	dan.customizablewatch.com	dan.customizablewatch.com	C=US, O=Let's Encrypt, CN=R3
2020-12-14T04:07:36.184	2020-12-14T03:07:36	2021-03-14T03:07:36	dan.customizablewatch.com	dan.customizablewatch.com	C=US, O=Let's Encrypt, CN=R3