Some troops types and creatures are protected by more than mere physical armour. They may be shielded by magical charms or blessings, given protection by the gods of the Warhammer world, or perhaps they are just astoundingly lucky.
Models with this sort of protection are referred to as having a Ward save or Ward. This type of save is quite different from an armour save and it is very important to understand the difference from the beginning.
Wards represent magical or divine protection which can save a warrior when armour would be of no use at all. Unlike an armour save, a Ward is never modified by Strength modifiers, etc. Even if a hit ignores all armour saves, a model with a Ward may still try to make its Ward save as normal. A model may only ever make one Ward save against each wound it has suffered.
Sometimes a model has both an armour save and a ward save. In this case, the model must take the armour save first and, if it is failed, the model is allowed to try to make a Ward save. No model can ever try to make more than one Ward save against a wound it has suffered. If a model has two Ward saves for any reason, use the better Ward save.