DNS stands for "Domain Name System". Simply put it is a service that translates an IP to a HostName (such as
UnderGroundNews.com).
DNS is a general-purpose distributed, replicated, data query service mainly used on Internet for translating hostnames into Internet addresses. Also, the style of hostname used on the Internet, though such a name is called a fully qualified domain name. DNS can be configured to use a sequence of name servers, based on the domains in the name being looked for, until a match is found.
The name resolution client (such as Unix's gethostbyname() library function) can be configured to search for host information in the following order: first in the local /etc/hosts file, second in NIS and third in DNS. This sequencing of Naming Services is sometimes called "name service switching". Under Solaris is configured in the file /etc/nsswitch.conf.
DNS can be queried interactively using the command nslookup. For more information on it, look up STD 13, RFC 1034, RFC 1035, and RFC 1591.
Ping is a network protocol that sends a message from one computer to another computer and waits for a reply, usually it is used to check if another computer on a network is reachable.