Straight From Wikipedia

Important Note: The Wikimedia Foundation does not own copyright on Wikipedia article texts and illustrations. It is therefore pointless to email our contact addresses asking for permission to reproduce articles or images, even if rules at your company or school or organization mandate that you ask web site operators before copying their content.

The licenses Wikipedia uses grant free access to our content in the same sense that free software is licensed freely. Wikipedia content can be copied, modified, and redistributed.

Copied Wikipedia content will therefore remain free under appropriate license and can continue to be used by anyone subject to certain restrictions, most of which aim to ensure that freedom. This principle is known as copyleft in contrast to typical copywrite license.

Here is the link:  http://en.wikipedia.org/wiki/Wikipedia:Copyrights#Reusers.27_rights_and_obligations