From A Wiki of Ice and Fire
In Ironborn culture a rock wife is an ironman's true spouse. A rock wife is ironborn. An ironman is allowed only one ironborn rock wife however he may keep several salt wives, non-ironborn women who have been captured on raids.
|“||"A man had his rock wife, his true bride. Ironborn like himself." ||”|
|“||His name, he said, was Adrack Humble, and he had a rock wife and three salt wives back on Great Wyk.||”|