Absolute Pressure refers to pressure measurements made on a scale where Absolute Vacuum = 0. *
An editor that displays in Absolute Pressure looks like this:
Column 10 is approximatly atmospheric pressure, slightly less due either to interpolation or the fact that even at WOT there will be some vaccuum.
Column 1 is somewhat arbitrary, and not true zero aka absolute vaccuum.
See also Map Sensor for the values the OEM Map Sensor is capable of reading.