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

Results formobile.marksilverstein.com

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2024-10-27T01:17:31.367	2024-10-27T00:18:58	2025-01-25T00:18:57	mobile.marksilverstein.com	mobile.marksilverstein.com	C=US, O=Let's Encrypt, CN=R10
2024-10-27T01:17:28.788	2024-10-27T00:18:58	2025-01-25T00:18:57	mobile.marksilverstein.com	mobile.marksilverstein.com	C=US, O=Let's Encrypt, CN=R10
2021-09-03T06:25:01.94	2021-09-03T05:25:01	2021-12-02T05:25:00	mobile.marksilverstein.com	mobile.marksilverstein.com	C=US, O=Let's Encrypt, CN=R3
2021-09-03T06:25:01.678	2021-09-03T05:25:01	2021-12-02T05:25:00	mobile.marksilverstein.com	mobile.marksilverstein.com	C=US, O=Let's Encrypt, CN=R3