PV stands for Protection Value and is the second of the values displayed in the bottom left corner, the first being DV. It represents the amount of damage your armor will absorb if you are hit. In the equip screen, for any given item the PV modifier will always be the second value displayed in square brackets. For instance, a standard issue suit of leather armor will display as "leather armor [+0, +2]", meaning it will add 2 to your PV rating.
PV helps survival of a character greatly in the early game. Even a few points will make a huge difference. Monsters such as rats or kobolds will rarely deal more than a few points of damage at a time in the very beginning, which doesn't take much armor to absorb completely. Other sources of PV are:
- Tough Skin talent and its successors, +1/+1/+2/+3;
- starting with 20, every two points of Toughness grant one additional point of PV, up to +20;
- blessed status, up to +3;
- negative corruptions: Stilts, -4;
- positive corruptions: Bronze bones, Stiff muscles, Scales, +3/+4/+8
- Tree star sign, +1;
- Fighters with their class powers, up to +25% to armor's PV
- Mental Shield, +(W + CL)/8
Beware - monsters are capable of bypassing PV with some hits, under an unknown set of circumstances, and some exist that are guaranteed to bypass PV on every hit. Claw bugs are likely to be the first of these you'll encounter.
See Monsters with penetrating melee attacks for a full list of monsters that always bypass PV.