Some Protestants employ terms such as Divine Service or service of worship, rather than the word Mass. For the celebration of the Eucharist in Eastern Christianity, including Eastern Catholic Churches, other terms such as Divine Liturgy, Holy Qurbana, and Badarak are typically used instead.
The English noun mass is derived from Middle Latin missa. The Latin word was adopted in Old English as mæsse (via a Vulgar Latin form *messa), and was sometimes glossed as sendnes (i.e. "a sending, dismission"). The Latin term missa itself was in use by the 6th century. It is most likely derived from the concluding formula Ite, missa est ("Go; the dismissal is made"); missa here is a Late Latin substantive corresponding to classical missio.
Historically, however, there have been other explanations of the noun missa, i.e. as not derived from the formula ite, missa est. Fortescue (1910) cites older, "fanciful" etymological explanations, notably a latinization of Hebrew matzâh (מַצָּה) "unleavened bread; oblation", a derivation favoured in the 16th century by Reuchlin and Luther, or Greek μύησις "initiation", or even Germanic mese "assembly". The French historian Du Cange in 1678 reported "various opinions on the origin" of the noun missa "mass", including the derivation from Hebrew matzah (Missah, id est, oblatio), here attributed to Caesar Baronius. The Hebrew derivation is learned speculation from 16th-century philology; medieval authorities did derive the noun missa from the verb mittere, but not in connection with the formula ite, missa est. Thus, De divinis officiis (9th century) explains the word as a mittendo, quod nos mittat ad Deo ("from 'sending', that which sends us towards God"), while Rupert of Deutz (early 12th century) derives it from a "dismissal" of the "enmities which had been between God and men" (inimicitiarum quæ erant inter Deum et homines).
The Catholic Church sees the Mass or Eucharist as "the source and summit of the Christian life", to which the other sacraments are oriented. The Catholic Church believes that the Mass is exactly the same sacrifice that Jesus Christ offered on the Cross at Calvary. The term "Mass" is generally used only in the Latin Church, while the Byzantine Rite Eastern Catholic Churches use the analogous term "Divine Liturgy" and other Eastern Catholic Churches have terms such as Holy Qurbana. Although similar in outward appearance to the Anglican Mass or Lutheran Mass, the Catholic Church distinguishes between its own Mass and theirs on the basis of what it views as the validity of the orders of their clergy, and as a result, does not ordinarily permit intercommunion between members of these Churches. Nevertheless, in a 1993 letter to Bishop Johannes Hanselmann of the Evangelical Lutheran Church in Bavaria, Cardinal Ratzinger (now Pope Benedict XVI) affirmed that "a theology oriented to the concept of succession, such as that which holds in the Catholic and in the Orthodox church, need not in any way deny the salvation-granting presence of the Lord in a Lutheran Lord's Supper." The Decree on Ecumenism, produced by Vatican II in 1964, records that the Catholic Church notes its understanding that when other faith groups (such as Lutherans, Anglicans, and Presbyterians) "commemorate His death and resurrection in the Lord's Supper, they profess that it signifies life in communion with Christ and look forward to His coming in glory."
Within the fixed structure outlined below, which is specific to the Ordinary Form of the Roman Rite, the Scripture readings, the antiphons sung or recited during the entrance procession or communion, and certain other prayers vary each day according to the liturgical calendar. For more information regarding the structure and history of the approved Extraordinary Form of the Mass in the Roman Rite, see Mass in the Catholic Church.
The priest enters, with a deacon, if there is one, and altar servers (who may act as crucifer, torch-bearers and thurifer). After making the sign of the cross and greeting the people liturgically, he begins the Act of Penitence. This concludes with the priest's prayer of absolution, "which, however, lacks the efficacy of the Sacrament of Penance". The Kyrie, eleison (Lord, have mercy), is sung or said, followed by the Gloria in excelsis Deo (Glory to God in the highest), an ancient praise, if appropriate for the liturgical season. The Introductory Rites are brought to a close by the Collect Prayer.
On Sundays and solemnities, three Scripture readings are given. On other days there are only two. If there are three readings, the first is from the Old Testament (a term wider than "Hebrew Scriptures", since it includes the Deuterocanonical Books), or the Acts of the Apostles during Eastertide. The first reading is followed by a psalm, either sung responsorially or recited. The second reading is from the New Testament, typically from one of the Pauline epistles. A Gospel Acclamation is then sung as the Book of the Gospels is processed, sometimes with incense and candles, to the ambo. The final reading and high point of the Liturgy of the Word is the proclamation of the Gospel by the deacon or priest. At least on Sundays and Holy Days of Obligation, a homily, a sermon that draws upon some aspect of the readings or the liturgy of the day, is then given. Finally, the Creed is professed on Sundays and solemnities, and it is desirable that in Masses celebrated with the people the Universal Prayer or Prayer of the Faithful should usually follow.