domain name system, or DNS
a service that translates computer names into Internet Protocol, or IP, addresses, and vice versa.
host name
a name that uniquely identifies a host in the domain.

For instance, server01 is the host name in the address

domain name
a unique name that identifies an entity on the Internet. Also known as a site name, it appears as part of the complete address of a web resource. It's usually registered by an organization as its web site address.

Primary DNS zone
When you add a zone to a DNS server as a primary zone, that DNS server is the primary server for the zone. Only one DNS server can host the primary zone, and all changes to the zone must be done through that server.
Secondary DNS zone
When you add a zone to a DNS server as a secondary zone, the DNS server hosts a read-only copy of the table from the primary server. The secondary DNS zone resource records are transferred by a process known as zone transfer.
address record
maps a host name to a 32-bit IPv4 address.
IPv6 address record
maps a host name to a 128-bit IPv6 address.

canonical name record
assigns one or more aliases to a host. So it enables a single host to have more than one name. This is useful if, for example, you want to host multiple web sites on a single server with one IP address.
mail exchange record
identifies the device hosting a mail server. A host often has more than one mail exchanger to increase the chances that mail will reach its destination successfully. The mail exchangers are recorded in order of priority, with the mail exchanger that should be accessed first listed at the top.

If the first mail exchanger is unresponsive, the second is tried, and so on.

name server record
delegates a DNS zone to use the given authoritative name servers.
pointer record
maps an IP address to a host name to allow for reverse lookup functionality.
start of authority record
contains authoritative information for a zone, including the primary DNS name server, contact details for the domain administrator, the domain serial number, and timers relating to refreshing the zone. There can be only one SOA file for each zone.
service locator record
can be used to identify a host that provides a specific service, such as a web or directory services server
client requests name resolution
A client sends a name resolution request to the DNS resolver when it needs to resolve a DNS name.

The resolver then generates a DNS name resolution request message, which transmits to the DNS server address specified during configuration.

the DNS server queries a root name server
When the DNS server receives a request, it checks if the requested name is in its DNS cache entries or its local DNS database. If so, it returns the IP address to the client. If there's no match for the name, the DNS server forwards the request to a root name server, asking it which DNS server it must query for the appropriate top-level domain.
the root name server responds
When it receives a request from a DNS server, the root name server responds with the IP address of the DNS server for the top-level domain in the name to be resolved.

the DNS server queries the top-level domain server
The original DNS server contacts the appropriate top-level domain's DNS server using the IP address supplied by a root name server. The top-level domain server reads the second-level domain of the requested name. If it can resolve the name, it sends the required IP address back to the requesting DNS server.
the DNS server queries other domain servers if necessary
If the top-level domain can't resolve the name because of additional levels in the FQDN, it sends the IP address of the second-level DNS server.
the host name is resolved
The communication between DNS servers continues until it reaches the level in the DNS hierarchy where a DNS server can resolve the host name.
the resolved address is returned to the client
The preferred DNS server provides the client with the IP address of the target host.