Magical Energy

"Magical energy" is a term used to describe energy found in many different forms. All of these various energies can be used to power spells and magic.

Storing & Retrieving Magical Energy

Magical energy be stored within a number of materials, but not all of them store it as well as others. Over time, energy dwelling within an object will slowly lose its potency, certain materials are better at keeping the energy at the same amount, namely metal and gems. On top of this, different materials can store more energy than others.
Once this energy is stored, it can be taken by any mage capable of manipulating magical energy. Unless an enchantment has been placed on the object to specifically stop this from happening.

Special Energy Sources

Some races gain magical energy from various methods other than their own wells of it.
All demons are capable of extracting magical energy from souls, in fact, all things that are capable of doing so are categorized as a "demon".
There are some rumored creatures able to wield energy provided to them by the sun itself (if the dimension they're in has one).