A domain is a complete subtree. In the DNS tree, a domain is everything under a particular point in the tree. Domains relate to the naming structure itself, not the way things are distributed. A zone is a pruned domain. Pruning occurs when zones are delegated.
Zones relate to the way the database is partitioned and distributed.
A label is one component of a domain name. Domain names in RRs which point at another name should always point at the primary name and not the alias. Legal characters in hostnames Domain names can contain almost any characters. The current releases of the BIND name server software enforce these restrictions. However, to check if a domain name has been registered and appears in the DNS, there are a couple of possible approaches.