The total correlation  shows the phase difference between the left and the right channel. The correlation plays a big role in how spatial your music sounds. A value of 1.0 means right and left signal have the same phase, -1.0 means a derivation of 180°.

See the screen shot for curve/phase relation of a sinus signal:

The total correlation should be in a range of 0.30 - 0.60 to have a good sound field, a Gonio-Meter like in PG-AMM-Lite can be very helpful to control the correlation.