A musical instruments is an instrument that can make musical sounds, it can be a traditional instrument created specifically to make music or something adapted to play music.
It’s theorized that using a starting pitch of A=432 Hz and a “just intonation” tuning method (scientific tuning) is more natural and mathematically symmetric than using A=440 Hz and “equal temperament” tuning (concert tuning).
Music theory and the basics of playing music (especially on the piano) can be understood through music intervals. All scales, chords, and most songs are based on intervals.
Whistle voice and falsetto are both high vocal registers that use alternative positions of the vocal cords and sound like different parts of a flute.
To quantize is to restrict something to a set of values. In digital music notes can be quantized to beats, in physics energy is quantized energy states.
A synthesizer is an instrument that uses electronics to produce sound. Sounds produced by a synthesizer are commonly triggered by a keyboard, but not always.