Process Data refers to a set of data added in series of business processes, and data is usually added (modified in some cases) when each task ends.

As a concept, whenever you make a "process" (precisely saying, a "Process Instance"), you have a set of Process Data to manage, and when the process ends, these Process Data is visible result, in another word "log". The process data group in the completed process is statistically analyzed, and used for the process improvement in most cases.

Because the principal purpose of Business Process Diagrams is to express flow of a business or a procedure, it is difficult to describe a format for Process Data in diagrams. When it is called "process definition data", it refers to "definition of processes" which a workflow engine interprets (in many cases, Process Diagrams and information about person in charge.