This is the number of seismic traces used from each of the seismic lines in the calculation. Seven is a good default. Seven traces mean that WinPICS takes three traces from either side of the intersecting trace plus the intersecting trace for a total of seven traces. WinPICS uses the sum of the seven traces in the calculation.
If you use too many traces in an area with lots of structure, the intersecting lines correlate poorly because the summation of traces does not reflect changes in dip.
What do you want to do?