The Mass is the gathering of the people of God to worship by meditating on the Scriptures (i.e. Liturgy of the Word) and on His life, death and resurrection (i.e. Liturgy of the Eucharist). The word "Mass" comes from the latin, "misa" and means to be sent out. That is because at the end of Mass, the Priest sends us out to bring the message of Jesus Christ to the world.
The Mass is also known as the Liturgy. Liturgy means the work of man. And in our Faith the work of man is to worship. Since the Mass is divided into two liturgies or ways to worship God, it is frequently called the Liturgy.
The Mass is also known as Our Lord's Supper. When Jesus Christ established the Mass on Holy Thursday, it was done in a table setting. The First Mass is frequently called the Last Supper because it was the last meal our Lord enjoyed before His sacrifice on the Cross. Therefore, the Mass is now frequently called the Lord's Supper.
The Mass is also known as the Eucharist. Our Lord also established the Holy Eucharist on Holy Thursday. Eucharist means "thanks giving" and refers to the fact that Jesus gave thanks for the meal before He established the Sacrament. But Eucharist now refers to the Sacrament in the form of bread and wine which is Our Lord's Body and Blood. This Sacrament is also known as Communion. And since the Mass ends with our participating in this Sacrament, the Mass is now frequently called the Eucharist.
See also the
Catechism.