Final answer:
Transubstantiation is the term describing the change of the bread and wine into the body and blood of Christ during the Eucharist, a belief held by Roman Catholics and Eastern Orthodox Christians.
Step-by-step explanation:
The term used when the bread and wine of the Eucharist are believed to change into the actual body and blood of Jesus Christ is Transubstantiation. This belief is particularly held by Roman Catholics and some Eastern Orthodox Christians, who view this transformation as a literal change, despite the appearance of the bread and wine remaining the same. The concept originates from the words of Christ during the Last Supper, as recorded in the Bible, where Jesus blessed the bread and wine and proclaimed to His apostles to do this in remembrance of Him.
The doctrine of transubstantiation is distinct from other interpretations within Christianity, such as that of the Calvinists, who regard the Eucharist as merely commemorative of the Last Supper.