"Mass" is one of the names by which the sacrament of the Eucharist is called in the Roman Catholic Church: others are "Eucharist", the "Lord's Supper", the "Breaking of Bread", the "Eucharistic assembly (synaxis)", the "memorial of the Lord's Passion and Resurrection", the "Holy Sacrifice", the "Holy and Divine Liturgy" and "Holy Communion". The term "Mass" is one of the most common in connection with Catholic Latin liturgical rites. It is used also of similar celebrations in Old Catholic Churches, in the Anglo-Catholic tradition of Anglicanism, in Western Rite Orthodox Churches, and in some Lutheran churches. But most Protestants prefer terms other than "Mass", which to them denotes Roman Catholic ritual and understanding of the Eucharist. For the celebration of the Eucharist in Eastern churches, including those in full communion with the Holy See, other terms such as the Divine Liturgy, the Holy Qurbana and the Badarak are normal.

For information on the theology of the Eucharist and on the Eucharistic liturgy of other Christian denominations, see "Eucharist" and "Eucharistic theology".

In physics, mass (from Greek μᾶζα "barley cake, lump (of dough)"), more specifically inertial mass, can be defined as a quantitative measure of an object's resistance to the change of its speed. In addition to this, gravitational mass can be described as a measure of magnitude of the gravitational force which is

when interacting with a second object. The SI unit of mass is the kilogram (kg).

In everyday usage, mass is often referred to as weight, the units of which are often taken to be kilograms (for instance, a person may state that their weight is 75 kg). In scientific use, however, the term weight refers to a different, yet related, property of matter. Weight is the gravitational force acting on a given body—which differs depending on the gravitational pull of the opposing body (e.g. a person's weight on Earth vs on the Moon) — while mass is an intrinsic property of that body that never changes. In other words, an object's weight depends on its environment, while its mass does not. On the surface of the Earth, an object with a mass of 50 kilograms weighs 491 Newtons; on the surface of the Moon, the same object still has a mass of 50 kilograms but weighs only 81.5 Newtons. Restated in mathematical terms, on the surface of the Earth, the weight W of an object is related to its mass m by W = mg, where g is the Earth's gravitational field strength, equal to about 9.81 m/s².

Liturgy (Greek: Λειτουργία) is the customary public worship done by a specific religious group, according to its particular traditions.

The word, sometimes rendered by its English translation "service", may refer to an elaborate formal ritual such as the Eastern Orthodox Divine Liturgy (Greek: Θεία λειτουργία) and Catholic Mass, or a daily activity such as the Muslim salat and Jewish services. As a religious phenomenon, liturgy is a communal response to the sacred through activity reflecting praise, thanksgiving, supplication, or repentance. Ritualization may be associated with life events such as birth, coming of age, marriage and death. It thus forms the basis for establishing a relationship with a divine agency, as well as with other participants in the liturgy. Methods of dress, preparation of food, olication of cosmetics or other hygienic practices are all considered liturgical activities.

The familiar sense of the word is an extension of the technical term in ancient Greek, leitourgia, signifying the often expensive offers of service to the people, and thus to the polis and the state. Through the leitourgia the rich carried a financial burden and were correspondingly rewarded with honours. The leitourgia became both mandatory and honorific, supporting the patron's standing among the elite. The holder of a Hellenic leitourgia was not taxed a specific sum, but entrusted with a particular ritual, which could be performed with greater or lesser magnificence. The chief sphere remained that of civic religion, embodied in the festivals: M.I. Finley notes "in Demosthenes' day there were at least 97 liturgical appointments in Athens for the festivals, rising to 118 in a (quadrennial) Panathenaic year." Eventually, under the Roman Empire, such obligations, known as Monera, devolved into a competitive and ruinously expensive burden that was not avoided^{[clarification needed]} when possible.