Here's Helm's ramblethread, it gives a great overview of what banding is.

basically, banding is where different pixel lines form a "staircase" sort of effect, i.e. hugging each other. AA can often turn into banding, if the pixels end up pretty much hugging the outline of something (I see some of that, for example, between the AA colour and outline in your Beef Patty piece).

banded-AA often looks fuzzy, or actually increases jaggies. To avoid it, you basically need to pay close attention to pixel clusters :)