Catholics like to use the term "Real Presence" when discussing the Eucharist and Jesus' presence in the consecrated bread and wine.
However, an outsider doesn't always know what that means or why Jesus' presence is called, "real."
Jesus' presence in the world
First of all, it is important to note that Jesus is present in a variety of ways in the world, as the Catechism of the Catholic Church explains:
"Christ Jesus, who died, yes, who was raised from the dead, who is at the right hand of God, who indeed intercedes for us," is present in many ways to his Church: in his word, in his Church's prayer, "where two or three are gathered in my name," in the poor, the sick, and the imprisoned, in the sacraments of which he is the author, in the sacrifice of the Mass, and in the person of the minister.
In many ways it can seem that Jesus is everywhere, present throughout all of his creation.
Yet, the Catechism proclaims, "he is present . . . most especially in the Eucharistic species" (CCC 1373).
Real Presence in the Eucharist
The Catechism goes on to say that Jesus' presence in the Eucharist is different than anything else in the world:
The mode of Christ's presence under the Eucharistic species is unique. It raises the Eucharist above all the sacraments as "the perfection of the spiritual life and the end to which all the sacraments tend." In the most blessed sacrament of the Eucharist "the body and blood, together with the soul and divinity, of our Lord Jesus Christ and, therefore, the whole Christ is truly, really, and substantially contained."
This unique presence is called "real" by the Church for a specific reason:
"This presence is called 'real' -- by which is not intended to exclude the other types of presence as if they could not be 'real' too, but because it is presence in the fullest sense: that is to say, it is a substantial presence by which Christ, God and man, makes himself wholly and entirely present."
The Eucharist remains a great mystery as the consecrated bread at Mass appears to be merely bread. Nothing changes in its exterior appearance, but the Catholic Church has consistently taught over the centuries that Jesus' "Real Presence" enters into the bread and wine in a miraculous way.
At times God has allowed certain miracles to bolster the faith of certain individuals, in which even the appearances change into Jesus' body and blood. It is a rare occurrence, but can reinforce our faith that Jesus is truly present at Mass.