#1
If you listen to keyboard players like Jordan Rudess and Jens Johannsen, their keyboards sound amazingly awesome. And in Guitar Pro, the instrument is labeled as a "Saw Wave". What is it?
#2
Its a Waveform where the pitch goes up then abruptly changes back down to the original pitch creating a shape similar to that of a Sawtooth.

But in reality I imagine that Rudess's sound is far more complex than that.
Rag Mop Do Do Duh DoDo Dedo Do!!!!!

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#3
it's a synth setting called saw wave. There's another one called square wave. I don't know the technicals about it but I've got a couple keyboards with both.
"There he goes. One of God's own prototypes. Some kind of high powered mutant never even considered for mass production. Too weird to live, and too rare to die."-Duke
#5
It's a basic waveform that is a staple of subtractive synthesis. If you googled "sawtooth waveform" you could probably find some audio examples.