A putative spouse is one who has a good faith belief that he or she is married but who is not legally married. An example will give a clearer picture.
A man and a woman get married either through a formal marriage or an informal, or common law, marriage. They live together for some time and accumulate property. One of them dies and the surviving spouse finds out after the death that the deceased spouse was previously married to someone else but never got a divorce. Because the deceased spouse was never divorced from his first spouse, the marriage to the second spouse is not valid. However, because the second spouse had a good faith belief that he or she was married, the second or putative spouse has rights to property that are similar to a spouse's rights to property in a valid marriage.