In Ironborn culture a rock wife is an ironman's true spouse, an ironborn woman.
An ironman is allowed to marry only one rock wife. However, he may keep several salt wives, non-ironborn women who have been captured on raids. Both are married by a priest of the Drowned God but the ceremony of a rock marriage is more solemn. The ironborn consider both the sons by a rock wife and by a salt wife to be legitimate, they all may inherit though the "salt sons" are placed behind the sons of a rock wife in the order of succession.
"A man had his rock wife, his true bride. Ironborn like himself."