Keep in mind this is my understanding of how they work and not necessarily how they actually work.  But here goes:

Weapon ranking:  The attack power the weapon will give to the equipped person.  Higher value = higher boost to their base attack or magical attack stat
armor ranking:  The amount that will be boosted for the defense and magical defense of the character equipped.

magic defense,:  How vulnerable the character will be tomagic based attacks.  Example:  Fighting a dark mage who deals fire damage, ice damage, or lightning damage to you.
  value:  The higher the value the more you'll get for the item when you sell it in the general store, or to the blacksmith...or whoever can buy things in the game.
and threaten enemy:  Not sure which this is, maybe the critical?  Just adds extra damage to your attacks, and if it protects against critical, you take less damage from a critical hit (a stronger base damage hit)
You can check in your character stats section to see how armor and weapons effect the stats of your character by hitting tab and going to the character stats section.  That helps a lot when you're confused with this sort of thing.
hope that helps