Mean Effective Pressure
It is the theoretical constant pressure which may be assumed acting on the piston during power stroke.
Indicated Mean Effective Pressure or Mean Indicated Pressure (MIP)
It is a pressure which on acting upon the piston, performs the same works as the actual pressure on the operating cycle. It is the ratio of the work done during the working stroke to the swept volume. It is determined graphically from a diagram or calculated from engine parameters.