Operator (physics)
In physics, an operator is a function acting on the space of physical states. As a result of its application on a physical state, another physical state is obtained, very often along with some extra relevant information.
The simplest example of the utility of operators is the study of symmetry. Because of this, they are a very useful tool in classical mechanics. In quantum mechanics, on the other hand, they are an intrinsic part of the formulation of the theory.
Read more about Operator (physics): Operators in Classical Mechanics, Concept of Generator, The Exponential Map, Operators in Quantum Mechanics