What are the parts of an orchestra?

Chicago Symphony

Orchestras are similar to living, breathing organisms.  They are composed of individuals that support the whole sound of the orchestra.  Additionally, there are multiply types of orchestras, including Symphony Orchestras, Chamber Orchestras and sinfoniettas. 

Maureen Buja gives nice explanation of the different types of orchestras and their uses at her blog, Interlude.

In many cities, there are multiple orchestras and although we might think that they differentiate themselves solely through their labels: London Philharmonic and London Symphony Orchestra, etc., they may also carry other names that differentiate them by size. The smallest orchestra is the “chamber orchestra.” It is made up of up to 50 members in total. The next size up is the “sinfonietta,” which has up to around 75 members. A full “symphony” or “philharmonic” orchestra has from 80 to 100 musicians. “Symphony” comes from the Latin meaning “concert” and “Philharmonic” comes from the Greek meaning “music loving.

What are the instruments in an orchestra?

Violins

Northwestern University Chamber Orchestra

Violas

Oberlin College Conservatory Violas

Cellos

City of Birmingham Youth Orchestra

Double Bass

Double Basses in Oregon Symphony