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

Results fornetflow.yyz2.oniaas.io

Resolver

Location

A

Name	TTL	Value
netflow.yyz2.oniaas.io	300	10.100.66.105

Name	TTL	Value
netflow.yyz2.oniaas.io	300	2605:6f00:aaaa:307:f816:3eff:fece:74d7

Name	TTL	Value
netflow.yyz2.oniaas.io	300	0 issue "letsencrypt.org ; validationmethods=dns-01; accounturi=https://acme-v02.api.letsencrypt.org /acme/acct/1447868266"
netflow.yyz2.oniaas.io	300	0 issuewild "letsencrypt.org ; validationmethods=dns-01; accounturi=https://acme-v02.api.letsencrypt.org /acme/acct/1447868266"