The term 'ADD TO STAFF' can be summarized as the process of hiring new employees. This involves finding suitable candidates, interviewing them, and then making a decision on who to HIRE. The four-letter solution for this term is HIRE, which is the action of bringing someone into a company or organization. Hiring new staff is an important part of any business, as it helps to ensure that the company has the right people in the right positions to help it grow and succeed.