Source: Dragon Magic
You learn to block damage from successful attacks, lessening the blows with spell energy.
Prerequisite: Draconic Heritage, Wizard level 1st.
Benefit: Whenever you cast an arcane spell, you gain damage reduction X/magic for 1 round (where X is equal to the level of the spell you just cast. For example, after casting fireball, you would gain DR 3/magic for 1 round.