What is staggering?

[komplex]

I'm brand new to the game and doing one of the challenge levels where you progressively get more debuffs. My fourth debuff is "Achilles" and it says that I can only kill enemies by staggering them. Problem is, I have no idea what that means. I don't know if I accidentally skipped over the text explaining what it is, but at this point I can do nothing besides kite and occasionally get one or two kills. Googling hasn't yielded any results yet so if someone could explain to me what it is that would be fantastic. Thanks!

[suibriel]

Enemies become staggered when you do enough damage to them! Some weapons and other gear stagger enemies more easily.

Hope that helps!

[Myrmeleon]

The most reliable way to stagger low tier enemies, especially in that level, is the Tristols secondary fire.