Difference between True Damage & Other damage?

True damage value stays true no matter what

If the skill says ''Does 340 true damage'' It means no matter how much armor or MR or ANYTHING the person has, it will do 340 damage.

Other damage gets reduced by resistences.

That's why Vayne is so hated. There are tanks literally building but Vayne melts through them like butter.

True damage cannot be amplified or mitigated by any means.

This includes:

• Resistances (i.e. Armor, MR)
• Percentage damage reduction (i.e. Exhaust, Maokai's ultimate, Alistar's ultimate)
• Flat damage reduction (i.e. Doran's Shield)
• Masteries (i.e. Double-edged Sword, Bounty Hunter, Battle Trance, Sorcery, Executioner)
• Damage amplification (i.e. Swain's Torment, Vladimir's ultimate)

Invulnerability is an exception.

True damage isn't affected by resistances, damage reduction, or damage multipliers.

To counter True Damage is to build Life, while there is %True Damage might be a pain. So keep in mind the type of True Damage is going on.

so everything that everyone else said + if u want to counter true damage you build health

Yes. Basically a way you can burn through tanks ignoring all their armor and mr or a way to execute someone. Ex: see low hp enemy at 500hp? Flash ult as lvl 11 cho and know you will kill them regardless of their mr. Unless they are fiora -- i'm not sure if her parry blocks the damage and returns it to you.