This is listed positive for eastern elongation, where the planet lags behind the Sun in their daily motion across the sky. L is the fraction of the disk that is illuminated. 1.0 is e.g. full moon, 0.0 new moon. This is negative if its south pole is inclined towards us. PA is the position angle of the planets rotation axis.
CM is the central meridian.
The planets have a system of planetocentric longitude similar to geographic longitude on the Earth. This is the planetocentric longitude of the centre of the disk as we see it from Earth.