In marriage, when a man refuses to engage with his wife in the same depraved sexual acts that they did early in the relationship. This is usually because he needs to think of her as a "respectable lady" and one does not do those sorts of things with someone you will bring home to that parents, or with the person who will be the mother of your children.
Wives whose husbands refuse to do anything but the most chaste (and infrequent) sex possible are said to have been "wife-zoned"
woman #1 "i just don't understand why my husband doesn't want to eat my pussy any more. He used to do it so much when we first met."
Woman #2: "honey, it means you've been wife-zoned"