Headquarters
Headquarters denotes the location where most, if not all, of the important functions of an organization are concentrated. The term is used especially with regards to Military organizations and large corporations.
Military headquarters
Military headquarters take many forms depending on the size and nature of the formation they command. Typically however they fall into the Tac, Main and Rear types (particularly within NATO).The tac headquarters is a small collection of staff and communicators usually very mobile, they exist to allow the Commander to get forward in an operations and command the key parts of it from a position where he can see the ground and influence his immediate subordinates.
The main headquarters is far less mobile and is often involved in both the planning and execution of operations. There are a number of staff assembled here from various staff branches to advise the Commander and control the various aspects of planning or the conduct of discreet operations. A main headquarters will usually have a Chief of Staff who coordinates the staff effort.
The rear headquarters is some distance from the battle or front line in conventional operations, its function is to ensure the logistical support to front line troops, it does this by providing medical, material, equipment and combat supplies by vehicle to where they are most needed.