GEO or Geo may refer to any of the following:

• Geo or gio, is a creek (inlet) or gulley in the Orkney and Shetland Islands
• GEO (newspaper), a popular scientific magazine
• Geo (microformat), a microformat for marking up WSG84 geographical coordinates in (X)HTML
• Geo (automobile), a brand of entry-level cars from General Motors
• Geo (marketing), a discipline within marketing analysis
• GEO 600, a detector for gravitational radiation
• Geo TV, a private television channel in Pakistan
• Global Environment Outlook, an environmental assessment produced by the United Nations
• Grupo Especial de Operaciones, a division of the Spanish police
• Gene Expression Omnibus, a scientific database for microarray data provided by the NCBI
• General Education Officer, the basic rank of teachers of the Ministry of Education in Singapore
• Genetically engineered organism, also known as genetically modified organism, an organism whose genetic material has been altered
• GEO, the IATA code for Cheddi Jagan International Airport
• Estadio Casas GEO, stadium in Mexicali, Mexico
• Geo, the Korean manhwa artist.

Geo. is sometimes an abbreviation of the name George.

• Geo Stelar is the main protagonist in Mega Man Star Force.

As a prefix, geo- is taken from the Greek word γη or γαια meaning "earth", usually in the sense of "ground or land". Geo- is thus a prefix for many words dealing in some way with the earth, including:

• Geocaching, an outdoor activity that involves using navigational techniques to finds geocaches
• Geocentric, a model of the universe that places the earth at its centre
• Geocoding, encoding coordinates in to features, images, web ages and other data records
  • See also Geotagging
• Geodesy, also known as geodetics, the study of the measurement and representation of the earth
• Geo-exchange, a heating and cooling system
• Geography, the study of the Earth and its features
• Geolocation, the science of determining the real-world location of a website or website visitor
• Geology, the study of the Earth's structure
• Geometry, the study of spatial relationships
• Geopolitics, the analysis of history, geography and social science with respect to international politics
• Geostationary orbit, a circular orbit directly above the earth's equator
• Geosynchronous orbit, an orbit that has the same period as the Earth's sidereal rotation
• Geothermal (geology), heat sources from within the Earth

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