A stall on a turbine blade occurs when air passes over it in such a way that the generation of lift rapidly decreases.

Individuals or companies that have a vested interest in a process.

Stainless steel is a group of iron-based alloys that contain a minimum of approximately 11% chromium, a composition that prevents the iron from rusting and also provides heat-resistant properties.

In hydrology, stage refers to the water level in a river or stream with respect to a chosen reference height.

The waste products from fuel combustion that exhausts to atmosphere via a dedicated pipe or trunking.

Stack effect or chimney effect is the movement of air into and out of buildings, chimneys, flue-gas stacks, or other containers, resulting from air buoyancy.

The pipe or trunking that conveys exhaust gases from the engine to the atmosphere.

Stable stratification of fluids occurs when each layer is less dense than the one below it.

An electrical output that is constant at all times within a specified value range.

A squirrel-cage rotor is the rotating part of the common squirrel-cage induction motor.

A squall line or quasi-linear convective system (QLCS) is a line of thunderstorms forming along or ahead of a cold front.

Sputter deposition is a physical vapor deposition (PVD) method of thin film deposition by sputtering.

A spring is an elastic object that stores mechanical energy.

A gas-liquid contactor used to achieve mass and heat transfer between a continuous gas phase (that can contain dispersed solid particles) and a dispersed liquid phase. This type of technology can be used for example as a wet scrubber for air pollution control.

Spontaneous combustion or spontaneous ignition is a type of combustion which occurs by self-heating (increase in temperature due to exothermic internal reactions), followed by thermal runaway (self heating which rapidly accelerates to high temperatures) and finally, autoignition.

Spontaneous fission is a form of radioactive decay that is found only in very heavy chemical elements.

In thermodynamics, a spontaneous process is a process which occurs without any external input to the system.

The spinning reserve is the extra generating capacity that is available by increasing the power output of generators that are already connected to the power system.

Spent nuclear fuel, occasionally called used nuclear fuel, is nuclear fuel that has been irradiated in a nuclear reactor (usually at a nuclear power plant).

A spillway is a structure used to provide the controlled release of water from a dam or levee downstream, typically into the riverbed of the dammed river itself.