DNS: Domain Name System. Ever wonder what's behind yahoo.com? For every single web address on the internet, there is a numerical IP address associated with it. The primary IP address for yahoo.com is 66.218.71.198. Would you rather remember yahoo.com or that numerical address? :) DNS tables do the job of matching those numbers to their corresponding domain name (yahoo.com). If a DNS tables becomes 'poisoned', it pretty much means that some corrupt data was inserted into the file and completely scrambled the data, rendering it useless.