Final Fantasy VI Encyclopedia
Basic Armor Stats:

Defense
An armor's defense determines how much damage you receive from physical attacks. The defense of all the armor you're wearing is added together to determine your total defense. See damage calculation for exactly how Defense affects the damage done.

Magic Defense
Magic Defense is just like Defense, except it affects damage done from magical attacks rather than physical attacks. See damage calculation for exactly how Magic Defense affects the damage done.

Armor special abilities and effects:

Use as an item to cast a spell
Amor with this effect: Flame Shld (Fire 3), Ice Shld (Ice 3), Thunder Shld (Bolt 3)

When an item casts a spell when used, the item is destroyed when used. The spell cast uses the same chance to hit and damage calculation as if cast by the character, with the exception that it skips steps 6 and 7 of damage calculation.

Only gains full power when Imp
Armor with this ability: TortoiseShld, Titanium, Imp's Armor
Armor with this effect only gains the Defense from the armor if the wearer is in Imp status. Magic Defense, Bonuses to Mblock, and all other bonuses are still obtained whether the wearer is an Imp or not, but the Defense is considered 1 if the wearer is not an Imp.

Raises Sketch Rate
Armor with this ability: Beret
Equipping an item with this ability increases your chance to succesfully sketch a monster by 50%. See the Sketch command for exact details.

Raises Control Rate
Armor with this ability: Coronet
Equipping an item with this ability increases your chance to succesfully control a monster by 50%. See the Control command for exact details.