Domain

Domain-A domain name is a sequence of "labels".
We are all reasonably familiar with domain names.  For example, "www.cavebear.com" is a sequence of the labels "com", "cavebear", and "www".
Notice that I have listed the labels in an order reverse from the way they appear in the domain name.  This represents the fact that the labels of a domain name have the more global part at the end.  Each label, as one moves from right-to-left represents a name within the scope of those labels which appear to its right.
Thus, the label "cavebear" is contained within the label "com".   And the label "www" is contained within "cavebear" (which is contained within "com".)
As you can guess, this nesting of names can be carried to considerable depth.
The most important, most global, rightmost label is not usually shown in domain name.   The "root", as it is usually called is simply ".".  (This is distinct from the dots used to separate labels.)
The DNS essentially translates a sequence of "labels" into a record of some sort.
The DNS contains a number of record types.  The most typical ones contain the IP addresses of host computers.  Other types of records contain aliases for labels, information about DNS servers, information about the location of exchangers for electronic mail, etc.
The way in which the DNS resolves a domain name query into a record is roughly as follows:
Suppose a user's computer wants to read a web page from host "www.cavebear.com".  That computer would contact a local name server, the address of which is configured into the user's computer by some administrative mechanism.