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

Results forbeta.dex.opoch.com

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2018-07-31T12:42:05.691	2018-07-31T11:42:04	2018-10-29T11:42:04	crypto.study	beta.dex.opoch.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2018-07-31T12:42:05.035	2018-07-31T11:42:04	2018-10-29T11:42:04	crypto.study	beta.dex.opoch.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2018-04-27T11:47:37.818	2018-04-27T10:47:37	2018-07-26T10:47:37	crypto.study	beta.dex.opoch.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2018-04-27T11:47:37.664	2018-04-27T10:47:37	2018-07-26T10:47:37	crypto.study	beta.dex.opoch.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2018-04-27T11:45:08.218	2018-04-27T10:45:07	2018-07-26T10:45:07	beta.findether.opoch.com	beta.dex.opoch.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2018-04-27T11:45:07.924	2018-04-27T10:45:07	2018-07-26T10:45:07	beta.findether.opoch.com	beta.dex.opoch.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3