ISO has many meanings:

• Iso is the stem of the Latin transliteration of the Greek word ίσος (ísos, meaning "equal"). The "iso-" prefix in English derives from this and means equality or similarity.
  • An isogram or an isorithm in cartography is a contour line, a reference to the fact that they connect points of equality. An isarithm is a contour map. An isobar is a curve on any map representing points on a surface that have the same atmospheric pressure.
• ISO is the International Organization for Standardization, a global federation of over a hundred national standards bodies with central secretariat in Geneva, Switzerland. The name ISO is derived from ίσος (see above) and is not an acronym for the organization's name in any of its working languages, though it is conventionally written in all capitals.
  • An ISO standard, an international standard published by the ISO. Although more than 15000 ISO standards have been published so far, each identified by a document number, the term "ISO" is in some fields commonly used just on its own as a shortname for something defined in one of these specifications. For example:
    • The ISO number in photography is the measure of film speed, or the sensitivity of photographic film to light exposure. It is defined in international standard ISO 5800.
    • An ISO image (*.iso) in computing is a disc image of an ISO 9660 file system.
    • ISO-standardised car radio connectors are referred to as "ISO Blocks" or similar.
• Iso automobile is an Italian automobile manufacturer, known for their Isetta bubble car.
• "Iso" also means "big" or "large" in the Finnish language.

ISO is a three-letter acronym which can stand for:

• The International Sugar Organization.
• The Insurance Services Office, an organization that supplies the US insurance industry with underwriting information.
• The Infrared Space Observatory, a now-defunct space telescope.
• The Imperial Service Order, awarded in the British honours system to long-serving members of the Civil Service.
• An Independent System Operator, an organisation that coordinates a regional wholesale electricity market in the US.
• The Institute for Social Organization, a US Jesuit think tank founded in 1943 and closed in the early 1960s.
• The International Socialist Organization, a political organization active in the United States.
• The International Socialist Organisation. the Australian branch of the International Socialist Tendency.
• "iso" or "i.s.o.", an abbreviation for "in search of" in personal advertisements.
• i.s.o., a gay-themed comic book derived both from "in search of" and the Greek iso, meaning equal.

NOTE: It does not stand for International Organization for Standardization in any language. See above for real origin of this organisation's name.