A symphony is a large-scale musical composition, usually with three or four movements. An orchestra is a group of musicians with a variety of instruments, which usually includes the violin family.
A symphony orchestra (often just called “a symphony” for short) is an orchestra that has both the number of players and types of instruments required to play a symphony.
And philharmonic just means “music-loving” and is often used to differentiate between two orchestras in the same city (e.g. the Vienna Symphony Orchestra and the Vienna Philharmonic Orchestra).
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