Noun

(en noun)

A number of things or persons being in some relation to one another.

* , chapter=5

, title= The Mirror and the Lamp , passage=Then everybody once more knelt, and soon the blessing was pronounced. The choir and the clergy trooped out slowly, […], down the nave to the western door. […] At a seemingly immense distance the surpliced group stopped to say the last prayer.}}

* {{quote-magazine, date=2013-07-19, author=(Peter Wilby)

, volume=189, issue=6, page=30, magazine=(The Guardian Weekly) , title= Finland spreads word on schools , passage=Imagine a country where children do nothing but play until they start compulsory schooling at age seven. Then, without exception, they attend comprehensives until the age of 16. Charging school fees is illegal, and so is sorting pupils into ability groups by streaming or setting.}}

(group theory) A set with an associative binary operation, under which there exists an identity element, and such that each element has an inverse.

(geometry, archaic) An effective divisor on a curve.

A (usually small) group of people who perform music together.

(astronomy) A small number (up to about fifty) of galaxies that are near each other.

(chemistry) A column in the periodic table of chemical elements.

(chemistry) A functional entity consisting of certain atoms whose presence provides a certain property to a molecule, such as the methyl group.

(sociology) A subset of a culture or of a society.

(military) An air force formation.

(geology) A collection of formations or rock strata.

(computing) A number of users with same rights with respect to accession, modification, and execution of files, computers and peripherals.

An element of an espresso machine from which hot water pours into the portafilter.

(music) A number of eighth, sixteenth, etc., notes joined at the stems; sometimes rather indefinitely applied to any ornament made up of a few short notes.

(sports) A set of teams playing each other in the same division, while at the same time not playing teams that belong to other sets in the division.

*

Noun

(en noun)

A device which separates a suspended, dissolved, or particulate matter from a fluid, solution, or other substance; any device that separates one substance from another.

Electronics or software that separates unwanted signals (for example noise) from wanted signals or that attenuates selected frequencies.

Any item, mechanism, device or procedure that acts to separate or isolate.

* {{quote-magazine, title=No hiding place

, date=2013-05-25, volume=407, issue=8837, page=74, magazine=(The Economist) citation , passage=In America alone, people spent $170 billion on “direct marketing”—junk mail of both the physical and electronic varieties—last year. Yet of those who received unsolicited adverts through the post, only 3% bought anything as a result. If the bumf arrived electronically, the take-up rate was 0.1%. And for online adverts the “conversion” into sales was a minuscule 0.01%. That means about $165 billion was spent not on drumming up business, but on annoying people, creating landfill and cluttering spam filters .}}

(mathematics, order theory) A non-empty upper set (of a partially ordered set) which is closed under binary infima (a.k.a. meets).

The collection of cofinite subsets of ''?'' is a filter under inclusion: it includes the intersection of every pair of its members, and includes every superset of every cofinite set.

If (1) the universal set (here, the set of natural numbers) were called a "large" set, (2) the superset of any "large" set were also a "large" set, and (3) the intersection of a pair of "large" sets were also a "large" set, then the set of all "large" sets would form a filter .