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

Results forwww.render-test.app.render.com

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2018-12-21T17:37:18.113	2018-12-21T16:37:17	2019-03-21T16:37:17	render-test.app.render.com	render-test.app.render.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2018-12-21T17:37:17.353	2018-12-21T16:37:17	2019-03-21T16:37:17	render-test.app.render.com	render-test.app.render.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2018-10-22T18:36:25.342	2018-10-22T17:36:24	2019-01-20T17:36:24	render-test.app.render.com	render-test.app.render.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2018-10-22T18:36:24.696	2018-10-22T17:36:24	2019-01-20T17:36:24	render-test.app.render.com	render-test.app.render.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3