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

Results forweb3.mech.disa.mil

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2020-01-29T03:10:05.725	2007-11-20T17:07:30	2010-11-20T17:07:30	web3.mech.disa.mil	web3.mech.disa.mil	C=US, O=U.S. Government, OU=DoD, OU=PKI, CN=DOD CA-17
2016-09-20T02:23:39.655	2016-07-19T15:34:09	2019-07-20T15:34:09	web3.mech.disa.mil	web3.mech.disa.mil	C=US, O=U.S. Government, OU=DoD, OU=PKI, CN=DOD ID SW CA-38
2013-10-26T12:57:21.001	2013-10-21T16:38:24	2016-10-21T16:38:24	web3.mech.disa.mil	web3.mech.disa.mil	C=US, O=U.S. Government, OU=DoD, OU=PKI, CN=DOD CA-28
2013-04-19T12:18:11.437	2010-10-26T21:15:50	2013-10-26T21:15:50	web3.mech.disa.mil	web3.mech.disa.mil	C=US, O=U.S. Government, OU=DoD, OU=PKI, CN=DOD CA-21