Domains are broken into "zones" for which individual DNS servers are responsible.
A domain represents the entire set of names / machines that are contained under an organizational domain name.
For example all domain names ending with ".com" are part of the "com" domain.
A zone is a domain less any sub-domains delegated to other DNS servers (see NS-records).
A DNS server could be responsible (authoritative) for all records under the "xyz.com" domain, but by defining NS-records for "abc.xyz.com", part of the domain is delegated to another DNS server - and perhaps even a different company/entity.
A zone contains exactly one SOA-record describing the general properties of the zone, and any number of other DNS records.
Entire zones can transferred from a primary DNS server to secondary DNS servers through Zone Transfers.
For an intranet (private network) DNS servers, a private root zone can be defined by leaving the zone name blank in the New Zone Wizard.
