Cross-class skill

From NWNWiki

Cross-class skills are skills that a given class has little experience with or that fall outside their expertise. Two skill points spent on a cross-class skill adds one rank in the skill. (Unlike pen and paper D&D, NWN does not track half ranks.) The maximum rank in any cross-class skill is equal to (character level + 3) / 2, or exactly half that of a class skill.