the action of functioning or the fact of being active or in effect

restrictions on the operation of market forces

the company's first hotel is now in operation

an act of surgery performed on a patient

I've never felt better since my bypass operation

an organized activity involving a number of people

a rescue operation

Operation Desert Storm

a process in which a number, quantity, expression, etc., is altered or manipulated according to set formal rules, such as those of addition, multiplication, and differentiation