An Aria (Italian for air; plural: arie or Arias in common usage) in music was originally any expressive melody, usually, but not always, performed by a singer. The term is now used almost exclusively to describe a self-contained piece for one voice usually with orchestral accompaniment. Perhaps the most common context for Arias is opera, although there are many Arias that form movements of oratorios and cantatas. Composers also wrote 'concert Arias', which are not part of any larger work, such as "Ah Perfido" by Beethoven, and a number of concert Arias by Mozart.   Wikipedia