Power immunity is a super-power. It is most commonly seen in media of the science fiction or superhero fantasy genres. It reflects the ability of a character to be able to resist certain types of attack as a natural application of their own biology. This may also be reflected through an external source such as a costume, power armor or some other device. It may also reflect the ability of an individual to be immune to their own super-powers.
For example: Bobby Drake is a mutant superhero known as Iceman. He has the ability to generate ice and lower the temperature of the surrounding area to below freezing temperatures. As a side-effect of this ability, Bobby is naturally immune to the effects of extremely cold temperatures. He suffers little risk of exposure and can walk about in the Arctic wearing nothing but a t-shirt and boxers without feeling any undue effects.