How would you define "ownership" in a relationship?

Someone I respect told me yesterday that “ownership” is always bad in a relationship. It was in the context of a discussion we were having about trying to change someone’s behavior toward other people, not necessarily as it affects oneself. Got me thinking. In what ways would you define ownership in an intimate relationship? Sexual possessiveness? Criticism? Enabling? Do you think it is always a negative? Can you be intimate with someone and not have it?