Final answer:
In the definition of Organizational Citizenship Behavior (OCB), 'voluntary' refers to actions that are discretionary and not formally required by an employee's job role, with no expectation of formal rewards.
Step-by-step explanation:
The term "voluntary" in the definition of Organizational Citizenship Behavior (OCB) refers to the discretionary behaviors that are not part of an employee's formal job requirements and that therefore, the employee is not obligated to perform. These behaviors are not typically recognized by the formal reward system, but they contribute to the efficient and effective functioning of the organization. OCB includes acts like helping coworkers, being involved in organizational activities, and going above and beyond the formal expectations of the job role. When employees engage in voluntary actions, they do so without the expectation of receiving any formal rewards, and the actions are often seen as a personal choice to contribute to the organizational environment and its goals.