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

Results forjoin.rev.team

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2021-05-29T06:53:25.488	2021-05-29T05:53:25	2021-08-27T05:53:25	join.rev.team	join.rev.team	C=US, O=Let's Encrypt, CN=R3
2021-05-29T06:53:25.217	2021-05-29T05:53:25	2021-08-27T05:53:25	join.rev.team	join.rev.team	C=US, O=Let's Encrypt, CN=R3
2021-03-30T06:35:46.306	2021-03-30T05:35:45	2021-06-28T05:35:45	join.rev.team	join.rev.team	C=US, O=Let's Encrypt, CN=R3
2021-03-30T06:35:45.96	2021-03-30T05:35:45	2021-06-28T05:35:45	join.rev.team	join.rev.team	C=US, O=Let's Encrypt, CN=R3
2021-01-28T20:12:40.657	2021-01-28T19:12:40	2021-04-28T19:12:40	join.rev.team	join.rev.team	C=US, O=Let's Encrypt, CN=R3
2021-01-28T20:12:40.447	2021-01-28T19:12:40	2021-04-28T19:12:40	join.rev.team	join.rev.team	C=US, O=Let's Encrypt, CN=R3