An anatomic bend normally means curve to straight (diagonally angling from the front of the bike (top) towards the rider (bottom)) to flat. The idea is that this provides a pistol grip type position when your hands are in the drop and covering the brakes.
Variable radius would, I guess, mean that a curved bar varies the degree of curve through the drop.
I can't really comment on the latter, as I've only used the classic bend and anatomic bars so far.