Concept
Agent
Also: Actor
Anything in a system that acts and reacts: a person, a team, a department, a piece of software, a rule.
In complexity thinking an agent is defined by what it does, not by what it is. Agents interact with each other and with constraints, and the system's behaviour emerges from those interactions. Many agents interacting with many others, with an almost endless number of possible combinations, is a hallmark of the complex domain.