A MAC Group is:

A MAC Group (Multiagency Coordination Group) is composed of senior officials, such as agency administrators, executives, or their designees, who are authorized to represent or commit agency resources and funds in support of incident activities.

A MAC group acts at an executive or policy level, supporting resource prioritization and allocation, and facilitates decision-making among elected and appointed officials and those responsible for managing the incident.

From an operational perspective, MAC Groups provide a structured framework for integrating the efforts of multiple agencies and jurisdictions, enhancing the overall effectiveness and efficiency of incident management and response.

They play a pivotal role in ensuring that the response efforts are cohesive, well-coordinated, and capable of addressing the complex challenges of major incidents or emergencies, thereby optimizing the use of resources and minimizing the impact on affected communities.

Source: https://training.fema.gov/emiweb/is/is800d/english/instructor%20guide/el0800.d%20ig.pdf