When Your Depth Of Field is in a Circle Of Confusion

I have recently read a few articles and guides that cover the depth of field (DOF) in photography, either about what it is or its application.  Initially I made cut and paste notes of those articles and was going to put together my own article based on those C+P words but I kind of figured ‘isn’t it better to do my own?’  After all most guide lines lead us to be confused in one way or another.
First what is depth of field?

To cut the...