A divorced person who wishes to remarry in the Catholic Church can apply to a church court for an annulment or “declaration of nullity.” This means that the sacramental bond of matrimony never existed in the earlier marriage because at least one of the parties was unwilling or unable to make and keep a promise of permanent, faithful, self-sacrificial marriage in which he or she modeled the love of Christ toward a spouse. A declaration that the sacrament did not exist does not mean that a loving marriage relationship never existed, and it does not make children illegitimate in the eyes of the church or civil law.
REFERENCE: Religion Stylebook