Dogmatically, the rebirth by which we become sons of God (John 3), identified with initial justification and sanctifying grace.
It is effected by the reception or desire of baptism, the sacrament of regeneration (Titus 3), and is sealed by the baptismal character which remains even after a death-bringing, or mortal sin.
Contrast this with the biological notion, i.e., repair of living tissue; with the metaphorical notion of efforescence; with the non-Christian idea of aspiration to new life, or release through metempsychosis; with the Pietistic idea of experience of conversion and of moral righteousness; with the old Protestant notion of Divine dissulation upon our sinfulness; with the Ritschlian notion of reconciliation following forgiveness.
Regeneration may also signify, in a cosmic sense, renewal of the Stoic world-cycle; and, in Christian eschatology, the resurrection of the dead (Matthew 19).
New Catholic Dictionary