Widows and orphans alike are defined by the severance of a relationship by death; the widow by the death of a spouse and orphan by the death of the parents.  A scriptural description of this is found in Exodus 22:22-24 where the Lord states in vs 24, "and My anger will be kindled, and I will kill you with the sword, and your wives shall become widows and your children fatherless".  A divorced woman is not a widow since her spouse still lives; if he dies, then she would be a widow.  A divorced woman is separated from her covenant spouse who is still living.  Unmarried is one who has never entered the covenant of marriage.