Relentless

Relentless is a  passive skill in Diablo III, unlocked at level 40.

In-game
The damage coming from a hit that actually brings the Barbarian below 35% Life is unaffected, the effect only becoming active afterwards. As of Patch 2.0.5, Relentless also shows a buff icon when active.

Note that both bonuses are multiplicative to other similar modifiers.