The term "music director" or "musical director" became common in the United States in the middle of the 20th century, following an evolution of titles. Early leaders of orchestras were simply designated as the "conductor." In the 1920s and 1930s, the term musical director began to be used, in order to delineate the fact that the person in this position was doing much more than just conducting, and to differentiate them from guest conductors who simply led one particular program or concert. George Szell, for instance, was appointed as "musical director" of the Cleveland Orchestra in 1946, and his position was so named until his death in 1970. His successor, Lorin Maazel, was given the title "music director." Other major American orchestras kept more current with the times and began using the simpler term in the 1950s and 1960s.