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

Results for*.staging.revstream.therevapp.com

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2019-04-28T15:33:18.907	2019-04-28T14:33:18	2019-07-27T14:33:18	staging.revstream.therevapp.com	*.staging.revstream.therevapp.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-04-28T15:33:18.907	2019-04-28T14:33:18	2019-07-27T14:33:18	staging.revstream.therevapp.com	*.staging.revstream.therevapp.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-04-28T15:33:18.745	2019-04-28T14:33:18	2019-07-27T14:33:18	staging.revstream.therevapp.com	*.staging.revstream.therevapp.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-04-28T15:33:18.745	2019-04-28T14:33:18	2019-07-27T14:33:18	staging.revstream.therevapp.com	*.staging.revstream.therevapp.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3