Cell on wheels (COW) is a portable mobile cellular site that includes a tower and transceiver as well as all other necessary equipment, carefully constructed on a trailer or truck that provides temporary network and wireless coverage to locations where cellular coverage is minimal or compromised. These mobile towers are usually used to create or boost a cellular network for a brief period, during an emergency, for a big event, or while a full tower is being built. COWs provide fully-functional service, via vehicles such as trailers, vans and trucks, to areas affected by natural disaster or areas with large user volume, such as major events. 

COW is also known as a site on wheels.