The Eucharist is the Sacrament of the Body and Blood of Jesus Christ. Holy Communion is a sharing in the Eucharist in which Christ is truly present. The priest, recalling the words and action of Jesus at the Last Supper, consecrates the bread and wine, which are changed , by the power of the Holy Spirit, into the Body and Blood of Christ. This is why the Church has traditionally employed the word "transubstantiation" to describe the change into the substance of Christ's Body and Blood. While the appearances of bread and wine remain, the Risen Lord Jesus is actually and Blood, soul and divinity.
To learn more on the Church teachings of the Eucharist, select the link below.