Guild Wars 2

Can someone explain to me what this buff really means and what it is the Boss gains from it ? the description is kind of vague and to general when you mouse over it.

Basically defiant makes them immune to “Crowd control” which is like, knockdowns and fears. Every time they are hit they lose 1 stack of defiant. At 0 stacks the next knockdown/fear will actually effect the boss, and then give them more stacks of defiant.

For example, some bosses have say 3 stacks of defiant.

That means you need 4 knockdowns before one of them will go through, at which point you need another 4 knockdowns before one will go through again.

It’s just there to stop things like event bosses from being perma-knocked down by the horde of players. But also to increase difficulty in dungeons (imagine if you just ran 5 KD warriors, you could constantly stop any boss from ever doing anything)