LSB - Least Significant Bit. Used in Prgoram changes typically.
MSB - Most Significant Bit. Ditto.
Data entry (like what data? dude?) - Umm, hard to say out of context, but
for us it's typically the rotating wheel used for scrolling. On some
synths it may be a slider, or knob.
sostenuto - Sustain.
variation - Hard to say out of context. Where do you see it?
timber - The other part of a sound aside from pitch and duration. Think
of a filter as something that changes a tone's timbre.
NPRN - Non Registered Parameter Number. How manufactures of midi gear get
around being limited to only 127 MIDI CC's and such.
RPN - Registered Parameter Number.
rEalm