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

Results forcatalog.selects.jp

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2018-07-10T10:11:25.105	2018-07-10T09:11:24	2018-10-08T09:11:24	stg.catalog.selects.jp	stg.catalog.selects.jp	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2018-07-10T10:11:24.978	2018-07-10T09:11:24	2018-10-08T09:11:24	stg.catalog.selects.jp	stg.catalog.selects.jp	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2018-07-10T09:19:11.996	2018-07-10T08:19:11	2018-10-08T08:19:11	*.selects.jp	*.selects.jp	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2018-07-10T09:19:11.808	2018-07-10T08:19:11	2018-10-08T08:19:11	*.selects.jp	*.selects.jp	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2018-07-10T08:49:28.745	2018-07-10T07:49:28	2018-10-08T07:49:28	*.selects.jp	*.selects.jp	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2018-07-10T08:49:28.62	2018-07-10T07:49:28	2018-10-08T07:49:28	*.selects.jp	*.selects.jp	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3