>>126846696 (OP)>>126848778>>126847782It can apply to how many simultaneous notes are played as well as to timbre - that is, how many different types of characters can be brought out of one instrument.
With synths, polyphony is how many layered notes it's capable of on top of the one note you're striking.
But with timbre, polyphony can also be how many voices the instrument is capable of imitating. Some instruments only ever sound like themselves and remain that way. Like a flute or sax. But a piano or guitar is many voiced. A classical guitar, without even any effects or amps, can be plucked to in multiple ways to produce different characters.
Piano too has many voices contained with it and why composers can practically create all the orchestra parts in a small "template" form all on a piano. You can imitate strings or the flute section or whatnot. Organ is the king of instruments, so called..and every pipe is calibrated to imitate other instruments. Although most people are used to hearing all of the pipes together and you get that booming church organ sound.
Synths:
https://www.youtube.com/watch?v=_IJUG4uujzA
Timbre
https://www.youtube.com/watch?v=V2zZl7Vifzw