This file defines minimum stat required to dual-class with this class. The first row (titles of columns ) is filled by the names of defined characteristics of PC (like MIN_STR = minimal strength ). The first column is filled by class/kits names. The crossings of the certain identifiers indicate if class/kit could be used with the characteristic of PC - used for character creation.
In IWD2 we have:

2DA V1.0
0
           MIN_STR    MIN_DEX    MIN_CON    MIN_INT    MIN_WIS    MIN_CHR
FIGHTER    0          0          0          0          0          0