You learn to block damage from successful attacks, lessening the blows with spell energy.
Prerequisites: Draconic Heritage, sorcerer 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.
Source: Dragon Magic, page 16.