(Warning: Possible spoilers ahead)
After reading my books, you will realize that magic plays an important role in both the day to day living and the many battles that occur. But there is more to magic than just casting spells, for, in the later books, there are magical items, such as weapons, mirrors, or even armour. So how does that work?
Magic in the world is defined as an innate power, usually passed down through the bloodline. It is a finite resource that is consumed and then slowly regenerated over time, often taking about ten hours to recover fully. Each mage has a limited amount of this magical energy, but through constant study and practice, they can enhance or grow this power, allowing more spells to be cast in a given amount of time.
The act of placing magic into an item is referred to as empowering. In Heir to the Crown, the druid, Albreda, empowers the warhammer, Nature's Fury, and later on, Aubrey empowers a magic circle in Wincaster, making it available for others to use.
The act of empowering takes a portion of the mage's power and places it within a separate object. This energy cannot be recovered by the mage, for once spent, it is permanently used up. Also, in order to accept the magic, the item must be constructed of a material that can contain the energy. In the books, this is either silver, gold, or sky metal, and the forged item must be crafted with great skill, else the magic will quickly dissipate. These are referred to as masterwork items.
Will there be more empowered objects in future books? You shall just have to wait and see.