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

Results fornotif.deb.dev.deeploop.com

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2019-08-03T20:27:48.964	2019-08-03T19:27:47	2019-11-01T19:27:47	deb.dev.deeploop.com	notif.deb.dev.deeploop.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-08-03T20:27:47.85	2019-08-03T19:27:47	2019-11-01T19:27:47	deb.dev.deeploop.com	notif.deb.dev.deeploop.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-06-04T19:51:59.96	2019-06-04T18:51:59	2019-09-02T18:51:59	deb.dev.deeploop.com	notif.deb.dev.deeploop.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-06-04T19:51:59.23	2019-06-04T18:51:59	2019-09-02T18:51:59	deb.dev.deeploop.com	notif.deb.dev.deeploop.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3