In the Italian opera world, the term is not only used for the conductor, but also for musicians who act as répétiteurs and assistant conductors during performances (maestro sostituto or maestro collaboratore). Even the prompter (maestro suggeritore) can be referred to by this title. (There is no agreement on how to address a woman conductor, as the feminate equivalent maestra connotes "schoolmistress" in Italian.)
By extension, it is used in English to designate a master in an artistic field, usually someone with strong knowledge who instructs others in the field, though the term may sometimes be conferred through sheer respect for an artist's works. The word is sometimes used in fine arts such as painting and sculpture, though there "master", as in Old Master, is far more common. Maestro is used in the sport of fencing, for a fencing instructor, and may be used in other sports to convey respect for an individual's skill.