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

Results forgcp.atomsecurity.io

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2023-08-08T13:58:10.363	2023-08-08T12:58:10	2023-11-06T12:58:09	whoami.gcp.atomsecurity.io	whoami.gcp.atomsecurity.io	C=US, O=Let's Encrypt, CN=R3
2023-08-08T13:58:10.183	2023-08-08T12:58:10	2023-11-06T12:58:09	whoami.gcp.atomsecurity.io	whoami.gcp.atomsecurity.io	C=US, O=Let's Encrypt, CN=R3
2023-08-08T13:58:00.122	2023-08-08T12:57:59	2023-11-06T12:57:58	registry.gcp.atomsecurity.io	registry.gcp.atomsecurity.io	C=US, O=Let's Encrypt, CN=R3
2023-08-08T13:58:00.018	2023-08-08T12:57:59	2023-11-06T12:57:58	registry.gcp.atomsecurity.io	registry.gcp.atomsecurity.io	C=US, O=Let's Encrypt, CN=R3
2023-08-08T13:57:00.398	2023-08-08T12:57:00	2023-11-06T12:56:59	gcp.atomsecurity.io	gcp.atomsecurity.io	C=US, O=Let's Encrypt, CN=R3
2023-08-08T13:57:00.207	2023-08-08T12:57:00	2023-11-06T12:56:59	gcp.atomsecurity.io	gcp.atomsecurity.io	C=US, O=Let's Encrypt, CN=R3