Appears to control default resistance values for classes/kits.
The first column lists class/kit identifiers.
The subsequent columns contain resistnce percentages for various damage types.
In IWD2 we have:

2DA V1.0
0
           		FIRE       COLD       ELEC       ACID       SPELL      MAGIC_FIRE MAGIC_COLD	SLASHING   BLUDGEONING PIERCING   MISSILE
BARBARIAN  		0          0          0          0          0          0          0         	0          0           0          0
CLERIC_BANE 		0          0          0          0          0          0          0         	0          0           0          0
CLERIC_TEMPUS 		0          0          0          0          0          0          0         	0          0           0          0
CLERIC_SELUNE 		0          0          0          0          0          0          0         	0          0           0          0
CLERIC_TALOS 		0          0          5          0          0          0          0         	0          0           0          0
WIZARD_ABJURER 		0          0          0          0          0          0          0         	0          0           0          0
WIZARD_CONJURER 	0          0          0          0          0          0      	  0          	0          0           0          0
WIZARD_DIVINER 		0          0          0          0          0          0          0         	0          0           0          0
WIZARD_ENCHANTER 	0          0          0          0          0          0          0          	0          0           0          0
WIZARD_ILLUSIONIST 	0          0          0          0          0          0          0          	0          0           0          0
WIZARD_EVOKER 		0          0          0          0          0          0          0         	0          0           0          0
WIZARD_NECROMANCER 	0          0          0          0          0          0          0          	0          0           0          0
WIZARD_TRANSMUTER 	0          0          0          0          0          0          0          	0          0           0          0