Electroacoustic Music Glossary

• Monophonic - only capable of playing one note at a time. An oboe is (for all intents!) a monophonic instrument, as was the first Moog synthesiser.
• Polyphonic - capable of playing more than one note at once.
  There are different degrees of polyphony:- if you were to spread yourself over all the keyboard of a piano, for instance, you could make all the notes sound at once. This isn't true for most electronic instruments which for reasons of cost only have a limited number of sound generation circuits. If you try to play more than that number, "note stealing" occurs whereby the first notes played, or (in more sophisticated instruments) the quietest notes will be replaced by the later/louder ones.