There's already a big glossary on music making to be found here: http://www.soundonsound.com/information/Glossary.php

Words that aren't to be found there (or in some other similar glossary if we know of another one) or have different meanings in the beast context, could be described here.

word list:

• instrument: an instrument is a CustomSynth? that uses the InstrumentInput? and InstrumentOutput modules (cited from tj)
• custom synthesizer:
• PostProcessor: a post processor is a CustomSynth? that applies an effect to either a whole track, or to a whole song

TODO: a lot of descriptions can be found in the quickstartguide - i (henning) should take the time to look them up and place them here.