Mass (disambiguation)

Scientific meanings

In physics, mass refers to the quantity of matter that manifests as inertia (resistance to acceleration) and as a source of gravitational attraction. Two operational notions are inertial mass and gravitational mass, which experiments show to be equivalent within measurement limits. The SI base unit of mass is the kilogram. In particle physics, related terms include rest mass (invariant mass) and the older notion of relativistic mass, the latter now discouraged in favor of invariant mass.

In chemistry and related fields, mass appears in measures such as atomic mass, molar mass, and the unified atomic mass unit (dalton), which quantify the mass of atoms, molecules, or amounts of substance.

Religious and musical meanings

As a proper noun, Mass denotes the principal Eucharistic service in many Christian traditions, especially the Roman Catholic Church, Anglicanism and some Lutheran communities. The word comes from the Latin missa, referring to the dismissal at the end of the rite. By extension, a Mass is also a musical composition that sets the liturgical texts (Kyrie, Gloria, Credo, Sanctus, Agnus Dei) for choir and sometimes orchestra.

Other uses and senses

• In mathematics and probability, mass can informally mean a weight assigned to points (for example, a probability mass function assigns probabilities to discrete outcomes).
• In everyday language, mass may mean a large quantity or a crowd ("the masses") or be used as an adjective in compounds (e.g., mass-produced, mass-market).
• In social and cultural contexts, "mass" appears in phrases like mass media, mass movement, or mass production to indicate wide scale or large audience.

History and distinctions

The word has independent roots in Latin for the liturgical Mass (missa) and for a lump or heap (massa), which helped give rise to the physical-science sense. Important distinctions to keep in mind: scientific mass is a measurable physical quantity distinct from weight (force due to gravity), while the religious Mass is a ceremonial event; musical masses are artistic settings of liturgical text; and many idiomatic uses emphasize size or collectivity rather than a precise physical property.

Knowing the context—science, faith, music, mathematics, or everyday speech—resolves most ambiguity when encountering the word "mass."