Shifts in the apparent charge stored on a floating gate (or other charge
storing element) of a non-volatile memory cell can occur because of the
coupling of an electric field based on the charge stored in adjacent
floating gates (or other adjacent charge storing elements). The problem
occurs most pronouncedly between sets of adjacent memory cells that have
been programmed at different times. To compensate for this coupling, the
read process for a given memory cell will take into account the
programmed state of an adjacent memory cell.