In a business, staff have different levels of responsibility and power. The directors and managers are at the top of the structure and the workers at the bottom. In between there are all the other staff, such as assistant managers and supervisors.
This describes communication between people on the same level within the organisation, for example manager to manager or worker to worker.
This is where people on different levels within the organisation pass information to each other, for example manager to worker, supervisor to director.