Short for Crescent wrench. Generically, an open-end adjustable wrench. In British, a spanner.
http://www.cooperhandtools.com/bran...1&att_id=CRE001&att1=Wrenches&att2=Adjustable
http://www.cooperhandtools.com/bran...1&att_id=CRE001&att1=Wrenches&att2=Adjustable