The act or process of operating or functioning. The state of being operative or functional: a factory in operation. A process or series of acts involved in a particular form of work: the operation of building a house. An instance or method of efficient, productive activity: That restaurant is quite an operation. An unethical or illegal business: a fencing operation for stolen goods. Medicine A surgical procedure for remedying an injury, ailment, defect, or dysfunction. Mathematics A process or action, such as addition, substitution, transposition, or differentiation, performed in a specified sequence and in accordance with specific rules. A logical operation. Computer Science An action resulting from a single instruction. A military or naval action, campaign, or mission. The headquarters or center from which a military action, flights into and out of an airfield, or other activities are controlled. The division of an organization that carries out the major planning and operating functions.