Unaffected is the term used in certain cards that are immune to the effects described in its effect description.
A well known example of a card that is unaffected by Trap Cards is "Elemental Hero Wildheart", examples of cards that are Unaffected by Spell Cards include "Horus the Black Flame Dragon LV6". Cards such as "Odin, Father of the Aesir" are unaffected by the effects of both Spell Cards and Trap Cards.
These cards can provide you with Field Advantage, when used in a cunning way such as using "Torrential Tribute" when your opponent summons a monster when you have "Elemental Hero Wildheart" in play.