A generation II reactor is a design classification for a nuclear reactor, and refers to the class of commercial reactors built until the end of the 1990s.

The General Conference on Weights and Measures is the supreme authority of the International Bureau of Weights and Measures, the inter-governmental organization established in 1875 under the terms of the Metre Convention through which Member States act together on matters related to measurement science and measurement standards.

Gelation (gel transition) is the formation of a gel from a system with polymers.

The gel point is an abrupt change in the viscosity of a solution containing a polymer.

A modern gel battery is a VRLA battery with a gelified electrolyte; the sulfuric acid is mixed with fumed silica, which makes the resulting mass gel like and immobile.

A gel is a semi-solid that can have properties ranging from soft and weak to hard and tough. Gels are defined as a substantially dilute cross-linked system, which exhibits no flow when in the steady-state.

A Geiger counter is an instrument used for detecting and measuring ionizing radiation.

Gearless wind turbines (also called direct drive) get rid of the gearbox completely.

This is the simplest form of rotary positive-displacement pumps.

GE Wind Energy is a branch of GE Renewable Energy, a subsidiary of General Electric.

In conventional wind turbines, the blades spin a shaft that is connected through a gearbox to the generator.

Gauge pressure is zero-referenced against ambient air pressure, so it is equal to absolute pressure minus atmospheric pressure.

Excessive battery charging causes electrolysis, emitting hydrogen and oxygen.

Gasoline gallon equivalent or gasoline-equivalent gallon is the amount of alternative fuel it takes to equal the energy content of one liquid gallon of gasoline.

Gasoline or petrol is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines.

A chemical process that converts a solid fuel into gases.

Gaseous diffusion is a technology used to produce enriched uranium by forcing gaseous uranium hexafluoride (UF6) through semipermeable membranes.

Gas-diesel engines utilise the diesel combustion process in all operational modes.

A gas-cooled reactor (GCR) is a nuclear reactor that uses graphite as a neutron moderator and a gas (carbon dioxide or helium in extant designs) as coolant.

Also known as a combustion turbine. Fuel is sparayed into compressed air which ignites and causes a high pressure gas flow which drives the turbine impellers.