This read-only value reports the Time-To-Live that was assigned to a cached negative DNS response, an authoritative no-such-name or no-data error, at the moment it was cached, typically copied from the SOA record's MINIMUM field or a smaller configured ceiling. An administrator consults it to understand how long the resolver will keep remembering that a particular name failed to resolve before retrying. For example, a long negative-cache TTL here would explain why a newly created DNS record isn't resolving yet even though it now exists upstream.