Guy:

I agree with you that processes, top level or otherwise are a connected series of activities intended to achieve a desired outcome.

You are right in that a process can exist without having any inputs or outputs - a clock being a good example.   In general though, processes have inpuits and outputs.   One of the "red flags" a data flow diagrammer looks for is processes (functions) without inputs or outputs.    Generally, such flags that the diagrammer is forgetting about a data flow.

Tony