Definition (1):
Staff authority gives the manager the right (authority) to advise other managers or employees. It creates an advisory relationship.
Definition (2):
Staff authority is the authority to serve in an advisory capacity (the authority to advise). Managers whose role it is to provide advice or technical assistance are granted advisory authority. Advisory authority does not provide any basis for direct control over the subordinates or activities of other departments with whom they consult: however, within the staff manager's own department, he or she exercises line authority over the department's subordinates.
Definition (3):
An advisory authority in which a person studies a situation and makes recommendations but has no authority to take action. Line managers get advice and other services from this authority. Some staff positions’ examples are finance, accounting, management information systems, purchasing, and taxation. Individuals in the staff positions have the power to assist and help the line functions like production and sales, but are entitled to no authority over them. For instance, as a staff authority, the cost accountant provides advice to the sales manager about which products possess the highest margins, and that’s why those are the most valuable products for selling.