Immune

A creature that is immune to a damage type (such as cold or fire), a condition (such as dazed or petrified), or another specific effect (such as disease or forced movement) is not affected by it. A creature that is immune to charm, fear, illusion, poison, or sleep is not affected by the nondamaging effects of a power that has that keyword. A creature that is immune to gaze is not affected by powers that have that keyword.

Published in Rules Compendium, page(s) 225.