A director is a person who is in charge of something important. The advertising director for a large company is the head of the department that places ads in newspapers and on TV.
Businesses have directors, and movies and plays also have directors, who oversee the way the actors deliver their lines and interpret the script. An orchestra's conductor can also be called a "musical director," and much like a film director, she guides the musicians and supervises their performance. The Latin root, dirigere, means "set straight."