Sweet/Sour spot?

Hey this might be obvious to some players, but I'm sure there are plenty of us who have no idea what this means. It sounds like maybe hitting with the hilt/handle instead of blade of axe or whatever. Or is it the place in the arc where you hit connects? Like on an overhead attack you pull back, swing over your head (first part) then you arc past the eyeline or chest height (Or more likely this is still part of the first "sweet spot") and maybe you have a back swing or a follow through to say the ground that could count as a lesser hit (So the sour spot?)? Some have 2 %s and some have 3. And they all seem to be better early.