The words locum tenens originate from Latin meaning "one holding a place". This phrase dates back to the middle ages when the Catholic Church provided clergy to parishes where there was no priest available. These travelling clergy were called locum tenens, placeholders for the churches they served. In later years the designation was used by doctors ("principals") who needed a person to temporarily fill their positions, should they not be available for a short period of time. It was only during the 1970s that the term was generally used by medical facilities where there was a shortage of medical doctors. Originally the staffing shortages were largely in sparsely populated areas, as high-income positions in large cities drew doctors away from the rural communities. Today locum tenentes are in demand nearly everywhere, whether in a city or a small town, when a doctor is not personally available to practice. Doctors in private practice may make use of a locum for several reasons; to take study leave or acquire new skills, to attend foreign or local congresses, or just for vacation leave.