A C.O.W. is a common acronym used in telecom industry for cell on wheels.

Cell on Wheel are considered low profile and portable because they are often mounted on trailers. They are often used in temporary OR emergency situation
Cell on wheels (COW) sometimes known as Site on Wheels is a portable mobile cellular site that provides temporary network and wireless coverage to locations where cellular coverage is minimal or compromised. 
COW cellular service is mostly provided to areas with non-functioning stationary cell towers. COW is also used for long-term placement by telecommunication companies when permanent site building is impeded by financing or infrastructure limitations.
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. 

STPL design manufacture and supply 30M and 40M COW in India.