I really don’t know the technical diff; bit I would think frizzy hair has coarse texture that is inherent or may be due to over processing. Flyaway would seem to be hair that is dry, or very fine, lightweight and easily movable.

I can’t believe I just answered this Q

@bythebay is pretty accurate.

Frizzy can be caused by coloring, or perming too often or using harsh chemicals.

Fly-away is most commonly caused by stripping the natural oils by over shampooing.