What does "orchestra" mean?

Additional senses

1. 2.(Mus.) (a) Loosely: A band of instrumental musicians performing in a theater, concert hall, or other place of public amusement. (b) Strictly: A band suitable for the performance of symphonies, overtures, etc., as well as for the accompaniment of operas, oratorios, cantatas, masses, and the like, or of vocal and instrumental solos. (c) A band composed, for the largest part, of players of the various viol instruments, many of each kind, together with a proper complement of wind instruments of wood and brass; -- as distinguished from a military or street band of players on wind instruments, and from an assemblage of solo players for the rendering of concerted pieces, such as septets, octets, and the like.
2. 3.(Mus.) The instruments employed by a full band, collectively; as, an orchestra of forty stringed instruments, with proper complement of wind instruments.