An orchestra is a group of musicians playing instruments together. They make music. A large orchestra is sometimes called a "symphony orchestra" and a small orchestra is called a "chamber orchestra". A symphony orchestra may have about 100 players, while a chamber orchestra may have 30 or 40 players. The number of players will depend on what music they are playing and the size of the place where they are playing. The word "orchestra" originally meant the semi-circular space in front of a stage in a Greek theatre which is where the singers and instruments used to play. Gradually the word came to mean the musicians themselves.