chicken wire

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A light-gauge galvanized wire fencing usually made with hexagonal mesh.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun uncountable a mesh of wire, usually galvanized, with a hexagonal pattern, generally used for making fences, especially for enclosures for small farm animals and pets.
• noun countable a type of such material, differentiated by material, coating, wire thickness, width, and mesh size.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a galvanized wire network with a hexagonal mesh; used to build fences