HR and Admin departments should be separate entities within an organization. For the smooth functioning of any professionally managed setup, there should be a clearly defined HR department and an Admin department. Although both departments work towards the betterment and overall development of employees, there may be instances where their roles overlap in the long run; however, they should remain distinct.
In manufacturing setups, there is typically no separate Admin department. Instead, there is a single department called the personnel department, which includes the HR department. One of the functions of the personnel department is administration. In service industries, there is usually no personnel department; they have HR departments. Until recently, service industries did not have a separate Admin department. However, nowadays, to ensure the smooth functioning of the office, the HR department has been split into HR and Admin. The HR department focuses on training, while the rest of the administrative tasks are handled by the Admin department.