“Orchestra”
is a broad term for any ensemble featuring a large proportion of
string instruments. There are two basic orchestras; chamber
orchestras (small) and symphony orchestras (big)
A symphony orchestra and a philharmonic are almost the same thing.
They are the relatively same size and they play the same kind of
music. The two terms help us tell different orchestras apart,
especially in cities that have multiple groups, as Brooklyn Symphony
and Brooklyn Philharmonic. Symphony orchestra is a generic term and
philharmonic orchestra is mostly part of a proper name.
Every philharmonic is a symphony, but not every symphony is a
philharmonic. Also, 'Pops' is an orchestra that usually
also plays (popular) show tunes.