A hydrogen infrastructure is the infrastructure of hydrogen pipeline transport, points of hydrogen production and hydrogen stations (sometimes clustered as a hydrogen highway) for distribution as well as the sale of hydrogen fuel.

Hydrogen fuel refers to the use of hydrogen gas (H2) as an energy carrier.

Hydrogen embrittlement also known as hydrogen assisted cracking or hydrogen-induced cracking, describes the embrittlement of a metal by diffusible hydrogen.

The hydrogen economy is an envisioned future in which hydrogen is used as a fuel for heat and hydrogen vehicles, for energy storage, and for long distance transport of energy.

As an energy buffer, hydrogen produced via water electrolysis and in combination with underground hydrogen storage or other large-scale storage technologies, could play an important role for the introduction of fluctuating renewable energy sources like wind or solar power.

A hydrogen bond (often informally abbreviated H-bond) is a primarily electrostatic force of attraction between a hydrogen (H) atom which is covalently bound to a more electronegative atom or group, and another electronegative atom bearing a lone pair of electrons—the hydrogen bond acceptor.

Hydrogen is the chemical element with the symbol H and atomic number 1.

Hydrofluorocarbons (HFCs) are man-made organic compounds that contain fluorine and hydrogen atoms, and are the most common type of organofluorine compounds. They are frequently used in air conditioning and as refrigerants; R-134a is one of the most commonly used HFC refrigerants. They do not harm the ozone layer as much as the compounds they replace, but they do contribute to global warming

Hydroelectricity, or hydroelectric power, is electricity produced from hydropower.

Conventional hydroelectric dams in most countries are highly regulated, with environmental reviews before construction and operational limits afterwards.

Hydrodynamics is the study of liquids in motion.

A catalytic chemical process widely used to remove sulfur from natural gas and from refined petroleum products, such as gasoline or petrol, jet fuel, kerosene, diesel fuel, and fuel oils.

See Chlorofluorocarbons (CFC’s).

Hydrocarbon exploration (or oil and gas exploration) is the search by petroleum geologists and geophysicists for deposits of hydrocarbons, particularly petroleum and natural gas, in the Earth using petroleum geology.

The hydrocarbon dew point is the temperature (at a given pressure) at which the hydrocarbon components of any hydrocarbon-rich gas mixture, such as natural gas, will start to condense out of the gaseous phase.

A hydrocarbon is an organic compound consisting entirely of hydrogen and carbon.

Hydraulics is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids.

Hydraulic head or piezometric head is a specific measurement of liquid pressure above a vertical datum.

A proppant is a solid material, typically sand, treated sand or man-made ceramic materials, designed to keep an induced hydraulic fracture open, during or following a fracturing treatment.

Hydraulic fracturing, also called fracking, fracing, hydrofracking, fraccing, frac'ing, and hydrofracturing, is a well stimulation technique involving the fracturing of bedrock formations by a pressurized liquid.