SRD:Resistance to Energy

''This is the ability that the term "energy resistance" refers to. If you are looking for the feat named "Energy Resistance", it can be found here.''

Resistance to Energy (Ex)
A creature with this extraordinary special quality ignores some damage of the indicated type each time it takes damage of that kind (commonly acid, cold, fire, or electricity), but it does not have total immunity. The entry indicates the amount and type of damage ignored. It doesn’t matter whether the damage has a mundane or magical source.

When resistance completely negates the damage from an energy attack, the attack does not disrupt a spell. This resistance does not stack with the resistance that a spell might provide.