Transubstantiation is part of the Roman Catholic Church. One part of the Christian faith is that they take communion at certain times of the year. This means that they eat a representation of Jesus’ body and they drink a representation of Jesus’s blood. In the Protestant faiths of Christianity, people believe that these food which is usually a piece of bread and a sample of grape juice or wine is symbolic of the body and blood of Jesus.
However, in the Catholic faith, they believe in transubstantiation where the bread and wine are transformed into the actual body and blood of Jesus when it is ingested into that person. This is one main difference between the Catholic and Protestant faiths.