Geographic information science, the academic theory behind the development, use, and application of geographic information systems

Geographic information system, a system for creating, storing, analyzing and managing spatial data and associated attributes

Gastrointestinal tract (or system), the digestive tract in humans and other primates

Greenland ice sheet, a vast body of ice covering most of Greenland

Geodesic interpolating splines in image registration

Gas insulated switchgear for electric power distribution

Garden International School, in Kuala Lumpur, Malaysia

Old Age Security-Guaranteed Income Supplement, a Canadian pension plan is a taxable monthly payment available to most older Canadians

Green investment scheme, a credit acquisition mechanism under the Kyoto Protocol

Goshen Intermediate School, in Goshen, New York

Groupe d'Intervention Spécial, a special operations unit of Algeria

Gruppo di Intervento Speciale, a counter-terrorist unit of the Italian Carabinieri

Gisborne Airport, Gisborne, New Zealand

Gippsland Independent Schools, an association of schools in the Gippsland region of Victoria, Australia