HP isn't having alot of arrows in the heart and keep moving (that's die hard). HP is the ability of a person to turn a large hit into a small one. A sword headed toward the midsection of a low HP person slices into the stomach and spills intestines. A sword headed toward the midsection of a high HP person slices the outside meat of the abdomen, damaging only muscle.

The HP system in Dnd is purposefully abstract, and HP really goes hand in hand with AC. That's why if a system is made where characters get AC bonuses as level increases, often times HP bonuses must also be obliterated.

As for the name of the feat:
Body of Iron?
Brawler?
Thick Skinned?
Homer's Meat Barrier of Brain Protection?