A Eucharistic miracle is a private revelation that is approved by the Church for devotion. A private revelation is different from public Revelation. Public Revelation ended with the death of the last apostle, St. John and is the totality of all that Christ has entrusted to His Church, expressed in apostolic faith in Scripture and Tradition from which the Magisterium draws all that it proposes for belief as being divinely revealed.
The Catechism of the Catholic Church defines private revelation as: Revelation made in the course of history which do not add to or form part of the deposit of faith, but rather may help people live out their faith more fully. Some private revelations have been recognized by the authority of the Church, which cannot accept so called revelations of faith that claim to surpass or correct the Revelation of Christ confided to his Church (CCC 67). Even if one does not accept a Eucharistic miracle, Christians are obliged to believe that God can work miracles and continues do so throughout history to the present day.
To date the Church has affirmed just over 100 Eucharistic miracles which have taken place in countries all over the world.