What exactly is the debuff damage please!

[iokunn]

Please tell me, because for me is only poison and that Ivy Effect that gasping root gives to summoners; in that the debuff items such as Xanos Jewels and the Amber Gems is just aimed to assassins and summoners /sick could it be that they created items only for those classes? Someone said in faction channel that stun is debuff as well but that is status effect, isn't it?  

 

So I am really confused because I do not know what is debuff in this game /sick in most games debuff is usually things that slow you down, root, decrease defense and such butt here is really unclear because the tool tip in your skills doesnt say applies debuff or something. 

 

Then I bought the Amber Pentagonal Gem and replaced with a Sapphire Pentagonal Gem and I compared my damage in PvE. I tested both of them and i did not see any difference in my DPS same base damage, same critical. 

 

So what in the hell does  the debuff damage do??????

 

[Suna]

It is purely pvp stat/infinite tower. Once target is cced you do more combo damage.