The difference between a supervisor and a manager is that a supervisor oversees the subordinate employees' work, while a manager is focused externally on making decisions for their unit. Supervisors focus more internally, where they ensure that the objectives and strategy created by the manager is implemented in the work space.
Both managers and supervisors work with subordinate employees, and are responsible for their overall success or failure within the company. The supervisor is typically responsible for the hiring and firing of employees, while the manager usually develops the unit's objectives that set the barometer by which the supervisor measures an employee's work results.
Some companies take the managerial duties and the supervisor duties to create a combined manager/supervisor role. When companies understand the core goals of leaders, managers and supervisors, then they can place hired employees in the role that will work best for them.
It is also important to give employees set roles. Some companies have positions with overlapping roles. This often confuses employees about their true role within the organization, and it makes creating objectives and implementing goals problematic. Tom Searcy of Inc. Magazine stresses the importance of companies developing concrete models with clear understanding when it comes to what role each employee plays in the success of the company.