The term for a piece of music written for an orchestra is "orchestral work" or simply "orchestration." This encompasses a wide range of musical forms, including symphonies, concertos, and overtures that are specifically composed to be performed by varied instrumental groups within an orchestra. Orchestral pieces can vary greatly in style and mood, often intended to convey complex emotions or stories through the interplay of the instruments. Composers from different eras such as Beethoven, Tchaikovsky, and Mahler have made significant contributions to this genre, creating timeless works cherished in concerts around the world, enhancing the cultural fabric of society.