Elemental Resistances
Elemental Resistances were a set of Attributes originally introduced with Final Fantasy XIV 1.0 (although the concept itself was introduced in and carried over from Final Fantasy XI). Increasing an elemental resistance attribute would decrease the damage taken by the corresponding attack of that elemental type. The six elements that could be guarded against were Fire, Ice, Wind, Earth, Lightning, and Water.
Theoretically, a character could have increased these attributes to guard against devastating attacks of a certain element as had been done in Final Fantasy XI; for example, water resistance could be increased to guard against attacks from Leviathan. However, few methods were available to alter these attributes. A small bonus (and small decrease) were assigned to two elements with the selection of a character's patron deity. The only way to semi-permanently increase these attributes was to meld Elemental Resistance materia. However, doing so would mean passing up materia that would have a far greater impact in terms of damage dealt.
As most enemy encounters never made use of these attributes in any meaningful way, and character progression was tied to increasing Item Level rather than sidegrades, these attributes were removed from the Character page and elemental materia was stripped of any stat bonuses in Patch 4.2.
Vestiges of these attributes still remain as a mechanic of shielding against enemy attacks, or conversely as a mechanic of increasing damage taken from certain attacks. For example, Scylla will drop water puddles that grant Fire Resistance Up that drastically decrease damage taken from her Ancient Flare.