Irregular

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Something that is irregular does not follow the expected pattern. The term is used in many different fields, with quite different meanings.

In astronomy, an astronomical object whose shape or behavior varies considerably from the archetype is called an irregular. This applies to irregular galaxy, irregular variable, asteroid, crater, orbit, planet, moon or natural satellite.

In language, it is applied to a word that do not follow the most common rules of the language, such as irregular verb, plural or spelling.

In business, law, politics, science and related fields, an irregular procedure, typically called an irregularity, is an action that does not completely follow the agreed standards, though it does not violate them. By itself, a single irregularity is of little consequence, but when many irregularities occur together, they may be signs of hidden fraud, misconduct or malfeasance. See creative accounting and 2004 U.S. presidential election controversy and irregularities for examples.

In manufacturing, an irregular is a product that does not meet the accepted levels of quality, but still available for sale, typically in secondary markets at a lower price.

In military terms, an irregular is a soldier who is not part of the official regular army, or does not follow regular army tactics. See irregular military.

In medicine, anything that does not follow the expected healthy pattern may be called irregular, such as irregular heartbeat or irregular menstrual cycle.

In mathematics, something that falls below the definition of the perfect archetype may be called irregular, such as irregular prime, polygon or polyhedron. The irregularity is an invariant of algebraic surfaces.

In chess, an opening that is little used and less studied is called an irregular chess opening.

See also