A philharmonic is a symphony orchestra or the group that supports it. A symphony is a large orchestra. An orchestra is a large group of musicians who play together on various instruments, usually including strings, woodwinds, brass instruments, and percussion instruments.
So, philharmonic and symphony orchestra are synonymous. Philharmonic comes from Greek words meaning ‘love of harmony’ and in this instance is a colloquial shortening of “philharmonic society” or “philharmonic orchestra.” The term only dates back to 1813. The term orchestra is much older and originally referred to the semicircular front part of a stage in ancient Greek theaters, which was where the chorus sang and danced. Orchestra evolved to mean the group of musical instrument performers in a theater.