Magic resistance

Magic resistance was an innate ability that could prevent magic from taking effect on a creature or person.

Various creatures steeped in magic, like the drow and most dragons and fiends, possessed magic resistance, as did strongly anti-magical ones. The likelyhood to negate any one spell or effect varied widely between different species.

Certain magical items, like a potion of magic resistance or robe of the archmagi, also granted this ability.

Background
Magic resistance was a concept used in the 1st and 2nd edition of Dungeons & Dragons. In the 3rd edition it was replaced by the two extraordinary abilities of spell resistance and spell immunity.