I have heard a lot of theories, but what i seek is a definite answer to what it does
1 theory for example is that its like counter is to crit rate, so it makes the chance of getting blocked lower, or it decreases the dmg given to an opponent who blocks you.
Break defense removes your opponents chance to block.
Block is when you take minimal damage and hit back.
Usually a Vanguard trait but a high block is never bad on any character.