If you have no idea what this means, don't worry, neither do I.
What I do know, however, is that a lot of people around KMail and are extremely happy about this :)
Basically the folks working hard on porting KDE PIM apps to Akonadi have reached one of their bonus mission goals: they've got rid of a very old, very obscure, tedious to maintain, mindboggling to work with (you get the picture, right?) legacy part of the mail handling framework.
Well, I guess bonus goal might give the wrong impression here. It is not less important than any of the primary mission objectives (to stay in game jargon). It is a bonus because it makes other things easier, boost your enthusiasm, lets you look forward for the challenges to come.
So, congratulations to the folks at KDAB. You rock!