Primary Resource is one of several terms that Diablo 4 likes to use liberally without actually ever spelling out what it means. Along with Resource Generation and Primary Resource Cost Reduction, you’ll see it in the descriptions of abilities, skills, and items.
When you see these references to Resource, you might be left scratching your head. At first, I thought it must be something to do with gathering materials for upgrading weapons. Because, you know, “resource” is another word for “material.” But it’s not in this case. It’s actually pretty simple: The confusing thing is just that Resource is a general term for something the game more often refers to by other, more specific names.