A person who operates a telephone switchboard. / A person who provides assistance in establishing a connection, or who provides information or takes messages via the telephone.

(military) That portion of a theater of war] which an army passes over in attaining its object.

(psychology) A technique of behavior modification through positive and negative reinforcement and positive and negative punishment.

(mathematics, physics) A differential operator,denoted ∆ and defined on ℝⁿ as 𝛥=∑ᵢ₌₁ⁿ(∂²)/(∂x_i²), used in the modeling of wave propagation, heat flow and many other applications.

A company that sells package holidays.

A subcontractor who may be a commercial carrier, but most often provides capacity (trucks and drivers, with or without trailers or chassis) to either commercial or private carriers under a contract for services.

(operations) The application of scientific methods and techniques to problems of decision making, especially in business management and government administration.

Any simple step in a multi-step chemical engineering process; examples include distillation, evaporation, mixing, filtration, crystallization etc.

(calculus) The study of calculus from the perspective of the theory of operators.

plural of operative word