Are the grass roots, supervisors and managers the human resources department?

These three positions are not exclusive to the human resources department.

Supervisor refers to a relatively basic management position, whose subordinates belong to the ranks of employees and are responsible for directly managing ordinary employees. The manager belongs to the middle management position and is responsible for managing the business of the supervisor and department. These two positions are different in the rank system of the company. The supervisor is the first rank after being promoted to a management position, while the manager is a position further promoted on the basis of the supervisor position.

The human resources department is responsible for human resources management such as recruitment, training, performance management, salary and welfare.