Hi:

I agree with David Wright: It all depends upon the conventions used in your company.  Another example: a function alternatively can be called objective, operation, process, task, action, activity, step, etc., etc.   

You can always find a solid agrument stating that, for example, a function means exactly X and a system means exactly Y.   The problem is that you can later discover a just-as-sound argument stating that a system means A and a function means Z. 

Often, what you will find is that the different opinions are based more on political considerations than logical.

Tony