third-level domain

a.k.a. subdomain

In the Domain Name System (DNS) hierarchy, it's the highest level underneath the second-level domains. It is that portion of the domain name that appears two segments to the left of the top-level domain; for example, the "products" in (Note: Third level domains are not the portion of an e-mail address that appears in front of the @ symbol.)

NetLingo Classification: Technical Terms