Transubstantiation
The substance of bread and wine becomes the body and blood of Christ.
This doctrine is actively contested between major traditions. Faithful Christians disagree.
What the traditions say
Dogma since Lateran IV. The substance changes while the accidents (appearance) remain. This is the Catholic church's definitive explanation of the Real Presence.
Some Orthodox theologians accept the term; others reject it as an overly philosophical Western import. The mystery of the change is affirmed, the mechanism is not defined.
Luther rejected transubstantiation while affirming real presence. The bread remains bread; Christ's body is present "in, with, and under" the bread.
Rejected. The Heidelberg Catechism Q80 condemned the Mass as "a condemnable idolatry." Christ's body is in heaven, not locally present in the elements.