According to Roman Catholic Church teaching, a sacramental character is an indelible spiritual mark (the meaning of the word character in Latin) imprinted by three of the seven sacraments: Baptism, Confirmation, and Holy Orders.
This teaching is expressed as follows in the Catechism of the Catholic Church, 1121:
The characters these three sacraments imprint are held to differ from each other, with each character remaining indelible, so that nobody can receive the sacrament in question more than once. The doctrine of the sacramental character is thus a particular expression of the long-established teaching that baptism, confirmation, and holy orders may not be repeated.
One who receives a lower grade of holy orders may receive a higher. Thus, though one who has been ordained a deacon may not again be ordained a deacon, he may be ordained a priest. Similarly, while a priest may not again be ordained a priest, he may be ordained a bishop. There is no higher grade to which a bishop may be ordained. Each higher grade is considered to confer a deepening or intensification of the character of holy orders.
If it is doubtful whether a person has received one of the three sacraments in question, the sacrament may be administered conditionally, but not, properly speaking, repeated.
The doctrine of the sacramental character was dogmatically defined at the 16th century Council of Trent, but was held for at least 1000 years before, and was written about by Augustine of Hippo.
The of the Catholic Church, 698 explains as follows the significance of the image of "seal", used as an alternative to that of "character":
irremovability in Spanish: Carácter sacramental
irremovability in Swedish: Sakramental karaktär