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

Results for*.gdg.io

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2018-08-13T17:59:00.776	2018-08-13T00:00:00	2019-08-13T23:59:59	*.gdg.io	*.gdg.io	C=GB, ST=Greater Manchester, L=Salford, O=COMODO CA Limited, CN=COMODO RSA Organization Validation Secure Server CA
2018-08-13T17:59:00.776	2018-08-13T00:00:00	2019-08-13T23:59:59	*.gdg.io	*.gdg.io	C=GB, ST=Greater Manchester, L=Salford, O=COMODO CA Limited, CN=COMODO RSA Organization Validation Secure Server CA
2018-08-13T17:58:43.786	2018-08-13T00:00:00	2019-08-13T23:59:59	*.gdg.io	*.gdg.io	C=GB, ST=Greater Manchester, L=Salford, O=COMODO CA Limited, CN=COMODO RSA Organization Validation Secure Server CA
2018-08-13T17:58:43.786	2018-08-13T00:00:00	2019-08-13T23:59:59	*.gdg.io	*.gdg.io	C=GB, ST=Greater Manchester, L=Salford, O=COMODO CA Limited, CN=COMODO RSA Organization Validation Secure Server CA