It means morally good, righteous or upright. It is an adjective often used to describe an unmarried woman who retains her virginity and remains chaste until she marries. There is a tendency, probably from King James English days to describe a good man as righteous and a good woman as virtuous. The noun from which it is derived, however, virtue, means a quality of character which is equally to be sought by both men and women who wish to be considered good people. For example, honesty is a virtue.