Combat Logistics Support can be defined as:

Combat Logistics Support is providing essential services to military organizations and their personnel in operational conditions.
US Department of Defense

People are the ultimate guarantors of combat readiness. Lack of access to basic services (such as lodging and dining facilities, medical aid, and recreation activities) can significantly impact the ability to function effectively for extended periods of time, and limit or prevent operations entirely.

Combat Logistics Support (CLS) is a multifaceted mission focused on providing operating forces a variety of necessary services. Recognizing CLS's importance to mission success, commanders identify, plan for, and deploy these services just as they plan their aircraft, weapons, spare parts, fuel, and other war-fighting needs.