There is often confusion when referring to orchestras, and it comes from the different names and sizes of them. All orchestras are formed to play instrumental music, but size does matter when discussing how they are named. A very small group of less than fifty is generally called a chamber orchestra. They were originally composed of musicians who mainly played string instruments for wealthy patrons in their homes. They are still popular at smaller gatherings, and many symphony musicians may spend time playing with one of these groups.

Symphony and philharmonic orchestras are comprised of more than fifty members, and they are sometimes defined as more than a hundred musicians. These orchestras play in large venues such as concert halls, indoor arenas and at large outdoor shows. A symphony orchestra is a generic name for any large group of musicians, and a philharmonic orchestra is one with its own proper title for identification purposes.