Serious ask HN: re; 'QUANTUM' -- I hear "quantum" used in so many various orthogonal ways, and I cant tell if they are all correct, or only one is.. but if onl

Serious ask HN: re; 'QUANTUM' -- I hear "quantum" used in so many various orthogonal ways, and I cant tell if they are all correct, or only one is.. but if only one is, I don't know which one it is> May you please define "quantum" for me ELI5?