Hi IXix, and thanks for replying.
A keyswitch is basically a special note that you can play on a virtual instrument: instead of producing a pitch/scrape/whatever, it silently changes the sound set for actual notes when you play them later. An example would be switching between legato, staccato, non vibrato and sul ponticello articulations for a solo violin. Typically they live around C0,C#0 etc or way up high™ for bass instruments.
Does that make things clearer?
Julio