Lame Delegation
A broken DNS delegation where a domain's listed nameservers do not actually answer authoritatively for the zone.
A lame delegation is what happens when a domain's NS records point at servers that either do not exist, do not respond, or refuse to answer authoritatively for the zone. The parent says "ask ns1.example.net for example.com," but ns1.example.net has no clue about example.com. Lame delegations cause slow lookups (resolvers wait for timeouts before trying the next NS), partial outages, and in some cases full unreachability. DNS Checker's own zone analysis flags lame delegations across the .com and .net zones as one of the most common operational bugs in the wild.