"A DNS zone is a portion of a domain name space using the Domain Name System (DNS) for which administrative responsibility has been delegated." (From Wikipedia, the free encyclopedia)
Questions dealt with "zone" deal with administration and configuration of so-called DNS-zones.
Wikipedia explains the two terms:
DNS refers to the Domain Name System, a hierarchical distributed naming system networked entitities such as computers.
A DNS zone is a portion of a domain name space using the DNS for which administrative responsibility has been delegated.