"The ritual, sacramental action of thanksgiving to God which constitutes the principal Christian liturgical celebration of and communion in the paschal mystery of Christ.  The liturgical action called the Eucharist is also traditionally known as the Holy Sacrafice of the Mass.  it is one of the seven sacraments of the Church; the Holy Eucharist completes Christian initiation (1322 ff.)  The Sunday celebration of the Eucharist is at the heart of the Church's life (2177).  Catechism of the Catholic Church