Excerpts from site:

There are several interpretations of the term "supervision", but typically supervision is the activity carried out by supervisors to oversee the productivity and progress of employees who report directly to the supervisors. For example, first-level supervisors supervise entry-level employees. Depending on the size of the organization, middle-managers supervise first-level supervisors, chief executives supervise middle-managers, etc. Supervision is a management activity and supervisors have a management role in the organization.

Occasionally, writers will interchange "leadership" and "supervision". Both activities are closely related. Supervision requires leadership. Leadership does not necessarily have to involve supervision.

New supervisors are often faced with a wide range of challenges, including that they:
Rarely have adequate training
Are often intimidated when faced with enforcing a wide range of policies and procedures
Rarely have enough time
Often feel very alone
Are sometimes overwhelmed and stressed out
Therefore, support and development are critical to new supervisors