Superheated steam is steam at a temperature higher than its vaporization point at the absolute pressure where the temperature is measured.

Superfluidity is the characteristic property of a fluid with zero viscosity which therefore flows without any loss of kinetic energy.

In physics, superheating is the phenomenon in which a liquid is heated to a temperature higher than its boiling point, without boiling.

The supercritical water reactor is a concept Generation IV reactor, mostly designed as light water reactor that operates at supercritical pressure (i.e. greater than 22.1 MPa).

A supercritical steam generator is a type of boiler that operates at supercritical pressure, frequently used in the production of electric power.

Supercritical steam – up to the 1,000–1,050 °F (538–566 °C); requires advanced materials.

Supercooling, also known as undercooling, is the process of lowering the temperature of a liquid or a gas below its freezing point without it becoming a solid.

Superconductivity is a set of physical properties observed in certain materials where electrical resistance vanishes and magnetic flux fields are expelled from the material.

Superconducting magnetic energy storage systems store energy in the magnetic field created by the flow of direct current in a superconducting coil which has been cryogenically cooled to a temperature below its superconducting critical temperature.

Superconducting electric machines are electromechanical systems that rely on the use of one or more superconducting elements.

A supercharger is an air compressor that increases the pressure or density of air supplied to an internal combustion engine.

A high-capacity capacitor with a capacitance value much higher than other capacitors, but with lower voltage limits, that bridges the gap between electrolytic capacitors and rechargeable batteries

A wide area network that is international or trans continental.

A portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light.

Sun-free photovoltaics is a photovoltaics technology which does not require sunlight to produce electricity.

Sun path, sometimes also called day arc, refers to the daily and seasonal arc-like path that the Sun appears to follow across the sky as the Earth rotates and orbits the Sun. The relative position of the Sun is a major factor in the heat gain of buildings and in the performance of solar energy systems.

The sun and planet gear is a method of converting reciprocating motion to rotary motion and was used in the first rotative beam engines.

Sulphur hexafluoride is an extremely potent and persistent greenhouse gas that is primarily utilized as an electrical insulator and arc suppressant.

A waste gas from the combustion of fuels in engines.

Sulfur (or sulfuric acid), byproducts of sulfur removal from petroleum which may have up to a couple of percent sulfur as organic sulfur-containing compounds.