Transubstantiation

Transubstantiation (in Latin, transsubstantiatio, in Greek μετουσίωσις metousiosis) is, according to the teaching of the Catholic Church, the change of substance by which the bread and the wine offered in the sacrifice of the sacrament of the Eucharist during the Mass, become, in reality, the body and blood of Jesus the Christ.

The Catholic Church teaches that the substance, or essence, of the Eucharistic offering (either bread alone, or bread and wine) is changed into both the body and blood of Christ.

All that is accessible to the senses (the outward appearances – species in Latin) remains unchanged. What remains unaltered is also referred to as the "accidents" of the bread and wine, but the term "accidents" is not used in the official definition of the doctrine by the Council of Trent. The manner in which the change occurs, the Catholic Church teaches, is a mystery: "The signs of bread and wine become, in a way surpassing understanding, the Body and Blood of Christ." The precise terminology to be used to refer to the nature Eucharist, and its theological implications, has a contentious history especially in the Protestant Reformation.

In the Greek Orthodox Church, the doctrine has been discussed under the term of metousiosis, coined as a direct loan-translation of transsubstantiatio in the 17th century. In Eastern Orthodoxy in general, the Mystery (Sacrament) of the Eucharist is more commonly discussed using alternative terms such as "trans-elementation" (μεταστοιχείωσις metastoicheiosis), "re-ordination" (μεταρρύθμισις metarrhythmisis), or simply "change" (μεταβολή).

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