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

Results for*.ptx.app

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2019-03-30T12:19:52.629	2019-03-30T11:19:51	2019-06-28T11:19:51	*.ptx.app	*.ptx.app	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-03-30T12:19:52.629	2019-03-30T11:19:51	2019-06-28T11:19:51	*.ptx.app	*.ptx.app	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-03-30T12:19:51.697	2019-03-30T11:19:51	2019-06-28T11:19:51	*.ptx.app	*.ptx.app	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-03-30T12:19:51.697	2019-03-30T11:19:51	2019-06-28T11:19:51	*.ptx.app	*.ptx.app	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-01-13T23:12:07.053	2019-01-13T22:12:05	2019-04-13T22:12:05	*.ptx.app	*.ptx.app	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-01-13T23:12:07.053	2019-01-13T22:12:05	2019-04-13T22:12:05	*.ptx.app	*.ptx.app	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-01-13T23:12:05.654	2019-01-13T22:12:05	2019-04-13T22:12:05	*.ptx.app	*.ptx.app	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-01-13T23:12:05.654	2019-01-13T22:12:05	2019-04-13T22:12:05	*.ptx.app	*.ptx.app	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3