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

Results for*.testerset.com

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2020-03-01T20:52:18.284	2020-02-27T00:00:00	2021-02-27T12:00:00	testerset.com	*.testerset.com	C=US, O=DigiCert Inc, OU=www.digicert.com, CN=Encryption Everywhere DV TLS CA - G1
2020-03-01T20:52:18.284	2020-02-27T00:00:00	2021-02-27T12:00:00	testerset.com	*.testerset.com	C=US, O=DigiCert Inc, OU=www.digicert.com, CN=Encryption Everywhere DV TLS CA - G1
2020-02-27T01:35:32.965	2020-02-27T00:00:00	2021-02-27T12:00:00	testerset.com	*.testerset.com	C=US, O=DigiCert Inc, OU=www.digicert.com, CN=Encryption Everywhere DV TLS CA - G1
2020-02-27T01:35:32.965	2020-02-27T00:00:00	2021-02-27T12:00:00	testerset.com	*.testerset.com	C=US, O=DigiCert Inc, OU=www.digicert.com, CN=Encryption Everywhere DV TLS CA - G1