Skill rank
From NWNWiki
A character's skill ranks in a skill is based on how many skill points a character has invested in a skill. For class skills, 1 point = 1 rank; for cross-class skills, 1 point = 1/2 rank. Ranks are the base to which other modifiers, such as skill focus and an ability modifier, are added.
Many skills can be used even if the character has no ranks in them; doing this is called making an untrained skill check.
