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

Results forwww.preview.davidmg.dev

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2019-10-06T22:05:26.414	2019-10-06T21:05:25	2020-01-04T21:05:25	preview.davidmg.dev	www.preview.davidmg.dev	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-10-06T22:05:25.687	2019-10-06T21:05:25	2020-01-04T21:05:25	preview.davidmg.dev	www.preview.davidmg.dev	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-08-07T20:10:20.753	2019-08-07T19:10:19	2019-11-05T19:10:19	preview.davidmg.dev	www.preview.davidmg.dev	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-08-07T20:10:19.547	2019-08-07T19:10:19	2019-11-05T19:10:19	preview.davidmg.dev	www.preview.davidmg.dev	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-06-08T17:21:26.882	2019-06-08T16:21:25	2019-09-06T16:21:25	preview.davidmg.dev	www.preview.davidmg.dev	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-06-08T17:21:25.787	2019-06-08T16:21:25	2019-09-06T16:21:25	preview.davidmg.dev	www.preview.davidmg.dev	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3