I explained that in post 715. It's the image of a spectrum I am using to explain my belief about belief. Perhaps a pretty picture would help.
Beliefs are based on which state of affairs we find to be most likely-- most probable. If we find something to be highly improbable, we have a negative belief-- we do not believe it. If we find something to be highly likely, we have a positive belief-- we do believe it.
There are different strengths of convicition in different beliefs. You may think something is only moderately or slightly likely, or that something is only slightly or moderately unlikely. Those two unlabeled hashmarks represent two equally strong beliefs, just at different ends of the spectrum (ie, 75% and 25%).
The 50% mark would indicate that you find something neither probable nor improbable. You have no opinion: both stances are equally convincing and equally absurd.