Defence(Defense) is a component which is used in almost all RPG's.
In Fiesta
In Fiesta, this is used as a stat which can make you more protected and therefore, not die easily. This Stat is a main ingredient to becoming a Tanker.
Location
This Stat can be found in the 'Character' icon, or you can just hit the hotkey , 'C'. See the picture to the right.
How is it Improved?
Defence can be improved in many ways. It can be improved by raising your END stat or by using a Def Scroll at any tier. Also, you can improve your item by wearing different Armours or Jewellery.
Overall
Overall, Defence can be cannged depending on your playstyle! if you want to be a high damage , but low defence, be a Glass-Cannon!(Pick a Mage as your class). Or, if you want to have low damage , yet high defence, be a Tank!(Pick a fighter as your class).