In the Domain Name System (DNS), third-level domains are the next highest level of the hierarchy underneath second-level domains. In a domain name, it is that portion of the domain name that appears two segments to the left of the top-level domain. For example, the "sterling" in "sterling.va.us". Third-level domains are not the portion of an email address that appears in front of the @ symbol-for example, the "web" in "
[email protected]" is not a third-level domain.