caterpillar track

from the GNU version of the Collaborative International Dictionary of English.

• noun an endless belt looped over several wheels, used in pairs in place of wheels to propel vehicles, such as tractors or military tanks, over rough ground.

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

• noun A continuous track in the form of a steel or rubber belt fitted instead of wheels to crawlers, bulldozers, tanks and similar off-road vehicles.

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

• noun an endless metal belt on which tracked vehicles move over the ground