Abjuration is the school or arcane magic that deals with protective and defensive magics, because of this it is a popular school for all magi, but particularly amongst those that are going into battle. A mage who specializes in abjuration is called an abjurer, though shield-mage and warder are also popular titles among those who practice the abjuration school. The most widely known spells with in the abjuration schools are the elemental wards and shields.
Elemental Wards are the most basic of abjuration spells. They are designed to protect the caster from a a specific element, often for only a few hits. The most popular three wards also happen to be the three most popular elemental schools used in offensive magic among magi. They are frost, fire, and arcane, other wards for other elements do exsist, but are not a widely known. Elemental Wards are taught to new magi in the hopes that they will use them if something goes wrong with their studying. They have limited use in battle where often times more than one elemental type is being used. Despite this limitation they are still considered an important part of any spell arsenal because they don't take much mana to cast.
Shields are the next step up from wards. They can block every kind of element, but also physical attacks too. There are several different kinds, but the most popular by far is the standard mana shield. A mana shield is exactly what the name implies, a shield made of mana. When the spell is cast it appears as a pale blue membrane is surrounding the caster. Experts in the abjuration field can make the shield transparent. The mana shields biggest drawback is that each blow recieved takes away from the casters mana reserves. Once the mana is gone, so is the shield and the ability to cast more spells and that is a dangerous position for a mage to find themselves in. In order to combat mana fatigue a new type of shield was invented. It blends an element with mana in order to perserve mana reserves. The spell is much more common now as it provides the same protection as the mana shield with less mana used. The most common element to blend with mana is frost.