DNS spoofing - Definition from the Hotspot Shield Glossary

Domain Name System spoofing is concerned with injecting false DNS data into a network cache with the intention of re-directing the network traffic away from the intended source destination.

DNS is responsible for translating domain names into IP addresses which allows network data to be routed to the correct nodes. DNS spoofing is a form of attack that will “poison” a DNS server by exploiting its vulnerabilities and importing incorrect data to the server which will result in the server traffic being re-directed incorrectly, either to other parts of the network it is not intended for, or back to the attacker - As a DNS server will cache any Domain/IP translations it processes, any incorrect information will be stored in that cache until the attack is sorted and the cache is cleared.