A mapping or function that acts on elements of a space to produce elements of another space (possibly and sometimes required to be the same space)
Commutation
When two operators commute, the order in which you apply them to a function does not change the final result. If and are two operators, they commute if for a given function .
In quantum mechanics, operators represent physical quantities or observables. If two operators commute, their corresponding physical properties can be measured at the same time with absolute precision.