headquarters

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun plural The offices of a commander, as of a military unit, from which orders are issued.
• noun plural A center of operations or administration.

from The Century Dictionary.

• The quarters or place of residence, permanent or temporary, of the commander-in-chief of an army.
• The residence of any military chief, or the place from which his orders are issued.
• Hence The place where one chiefly resides or carries on business.

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

• noun plural The quarters or place of residence of any chief officer, as the general in command of an army, or the head of a police force; the place from which orders or instructions are issued; hence, the center of authority or order.
• noun plural The main office from which an organization such as a commercial enterprise is managed; -- usually where the chief executive officer works.

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

• noun The military installation from which troops are commanded and orders are issued; the military unit consisting of a commander and his support staff.
• noun The center of an organization's operations or administration.
• noun A place of concentrated activity or influence.

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

• noun (plural) a military unit consisting of a commander and the headquarters staff
• noun the military installation from which a commander performs the functions of command
• noun (usually plural) the office that serves as the administrative center of an enterprise