Function Analysis challenges the assumptions most people make about how a product or service satisfies a need. Asking How and Why a function accomplishes the need. Only then can you begin to understand what is necessary to accomplish the function.
Function is the intent or purpose that the product, process or service is expected to perform in it's normal manner.
(Described using and active verb and a measurable noun).
Function is the end result desired by the customer ...
it is what the customer pays for!