The term "operation" is the key concept of the discipline of operations research, as its very name suggests. Within the discipline, however, the term carries a strictly defined meaning. Since operations research was originally developed to support military decision-making, the term is closer in meaning to "military operation." The object of modeling in operations research is an operation — a purposeful and controlled activity that employs a specific set of resources under given constraints.
An operation is an organized course of action governed by a single plan and directed toward the achievement of a stated goal (Wentzel, Ye. S.).
Based on this definition, two features deserve attention.
The first feature is that an operation is inherently activity-based; it rests on three components: the goal, the means, and the object of the activity (that at which the activity is directed).
The second feature is that an operation can be represented as a system of actions or as a goal-directed system. The concept of a unifying plan implies the existence of a certain plan and the effort devoted to its development.
An operation is always a controlled undertaking: a decision-maker (DM) determines how to select certain parameters of the operation, and the choice of these parameters affects the achievement of the goal. The specific choice of parameters that depend on the DM constitutes a decision. The optimal decision is the one that, by one criterion or another, is preferable to the alternatives. The methods of operations research are designed for the qualitative and quantitative justification of optimal decisions.
As operations grow in scale and complexity, one is increasingly confronted with problems of optimal control of "complex systems" — systems comprising a large number of elements and subsystems organized on a hierarchical principle. Operations research is closely linked to the systems approach and to decision theory.