Reordination is the repetition of an ordination ceremony for a Bishop, priest, or deacon because there are serious grounds for doubting the validity of a previous ordination. The term is inaccurate, since Sacred Orders, once conferred, cannot be repeated.
In the Roman Catholic Church, the Sacrament of Holy Orders is not repeated for a validly ordained priest who repents after being a schismatic, a heretic, a grave sinner or an apostate. The contrary teaching was promoted by the Donatists in the late second and early third centuries. According to the Donatists, if a man denied his Catholic Faith under persecution and later repented, he had to be reordained. This same error has penetrated into some circles of the Eastern Orthodox Churches which are separated from Rome. Behind this error is a denial that some Sacraments confer an indelible character on those who receive them.
To clarify, once a person is baptized, or confirmed, or ordained, he cannot be rebaptized, reconfirmed, or reordained. This is why the now common term “laicization of priests” is erroneous. A priest is never reduced to the lay state no matter what happens in his life. He may lose his faith, or lapse into a life of immorality, or become a sworn enemy of the Catholic Church. Nevertheless, even though the term “laicized” is commonly used to refer to a priest who has left the ministry of the priesthood, he remains a priest for all time and into eternity. (For Advanced Course lesson 23.)