In the Domain Name System (DNS), the next highest level of the hierarchy below the second level domains. In a domain name, that part of the domain name that appears two segments to the left of the top-level (or first level) domain. For example, the "verio" in verio.va.us. Third level domains are not the part of an e-mail address that appears in front of the "at" (@ )symbol. For instance, the support in
[email protected] is not a third level domain.