From IPAPI

There are many facets of what a process really is that are not included within most approaches to process management. One of the most prominent of these facets is the interaction within a process between the people, systems and machines (Process Actors) in organizations that get things done.

IPAPI Definition

Process Actors – Process Actors are the people, systems and machines that perform the work of a process. For every interaction in a process there are two Process Actors.

Overview

Consider if you will that every process is many ways a real life drama, one that organizations play out every single day. Each of these dramas includes a number of actors, the process actors that perform in the process drama.

Some of these actors are people; employees of the organization, the customers of the organization and the people who make up the business to business relationships the organization also relies on to get things done.

Other actors are systems; the software organizations use to help them get work done. There are also machines that have process actor roles, from such simple machines as telephones, facsimile, and printers to more advanced machines that have compound functions – many including varying degrees of embedded automation.

All of these can be process actors.