System-specific impulse, often denoted as \(I_{sp}\) or just \(I_s\), refers to the efficiency of a rocket engine or propulsion system when considering its entire setup, including all components and not just the engine itself. This concept extends the traditional notion of specific impulse by factoring in the contributions and effects of various system elements such as fuel, oxidizers, and auxiliary systems that may affect overall performance.

Susceptance is a measure of a circuit's ability to conduct alternating current (AC) in response to an applied voltage. It is the reciprocal of reactance (denoted as \(X\)) and is usually represented by the symbol \(B\). In electrical engineering, susceptance is typically used to describe the behavior of components such as capacitors and inductors, which store and release energy in an AC circuit.

Surface stress refers to the additional mechanical stress that occurs at the surface of a material due to the presence of surface atoms, which behave differently than those in the bulk of the material. This phenomenon is particularly important in materials science and nanotechnology, as the physical and chemical properties of materials can change significantly at the nanoscale, where the surface-to-volume ratio is high.

Surface power density generally refers to the amount of power (energy per unit time) that is distributed over a specific surface area. It is a common concept in various fields, including physics, engineering, and materials science, and is often expressed in units such as watts per square meter (W/m²).

Suction is a physical phenomenon that describes the creation of a pressure difference between two areas, resulting in the movement of a fluid (liquid or gas) towards a region of lower pressure. It is often associated with the action of drawing in or removing a substance, such as air, liquid, or particles, through a vacuum or an area of lower pressure.

Strangeness is a property of particles in the realm of particle physics, specifically relating to the presence of strange quarks within particles. It is a quantum number that describes how much a particle deviates from being a "normal" baryon or meson regarding the number of strange quarks it contains.

Stiffness is a mechanical property of materials that describes their resistance to deformation under applied loads. It quantifies how much a material will deform (strain) when a force (stress) is applied to it. The greater the stiffness of a material, the less it deforms when subjected to a given force. Stiffness can be defined in various contexts, particularly in engineering and mechanics.

Standard gravity, often denoted by the symbol \( g_0 \), is a physical constant that represents the acceleration due to Earth's gravity at the surface. It is defined as approximately \( 9.80665 \, \text{m/s}^2 \) (meters per second squared). This value is based on the standard conditions and represents the mean gravitational acceleration experienced by objects at sea level at 45 degrees latitude.

The speed of sound is the distance that sound waves travel through a medium (such as air, water, or solid materials) in a given period of time. In general, the speed of sound varies depending on the medium through which it is traveling, as well as environmental conditions such as temperature and pressure. In air at sea level and at a temperature of about 20 degrees Celsius (68 degrees Fahrenheit), the speed of sound is approximately 343 meters per second (1,125 feet per second).

Speed is a scalar quantity that measures how fast an object is moving, quantifying the distance traveled per unit of time.

Spectral Power Distribution (SPD) refers to the representation of the power of different wavelengths (or frequencies) of light emitted by a source. It essentially describes how the intensity of light varies across the spectrum, which can include ultraviolet (UV), visible, and infrared (IR) ranges.

Specific weight is a measure of the weight of a substance per unit volume. It is typically expressed in units such as newtons per cubic meter (N/m³) or pounds per cubic foot (lb/ft³).

Specific impulse (often denoted as I_sp) is a measure of the efficiency of rocket propellants. It is defined as the thrust produced per unit weight flow of the propellant, and it is typically expressed in seconds. Specifically, specific impulse indicates how effectively a rocket engine converts propellant into thrust, providing a measure of the engine's performance.

Specific force is a term used primarily in engineering and physics to refer to the force acting on a unit mass. It is generally expressed as force per unit mass (such as newtons per kilogram, N/kg) and is often used to analyze dynamics, particularly in relation to acceleration, gravity, and other forces acting on a system.

Specific detectivity (D\*_n) is a measure used to characterize the performance of infrared detectors and other types of photodetectors. It quantifies the ability of a detector to sense weak signals in the presence of noise, and is defined as the ratio of the detector's responsivity to the noise current.

Specific density, commonly referred to as "specific gravity," is a dimensionless quantity that compares the density of a substance to the density of a reference substance, typically water for liquids and solids, and air for gases. It is defined as the ratio of the density of the substance to the density of the reference substance at a specified temperature and pressure.

Sound pressure is a measure of the local pressure variation from the ambient atmospheric pressure caused by a sound wave. It is typically expressed in pascals (Pa) and is a key parameter in acoustic measurements. When a sound wave travels through a medium (such as air, water, or solid materials), it causes fluctuations in pressure, which are perceived as sound.

Sound power is a measure of the total energy emitted by a sound source per unit of time. It represents the overall intensity of the sound produced, independent of the distance from the source or how the sound is perceived by an observer. Sound power is typically measured in watts (W) and is often expressed in decibels (dB) relative to a reference power level.

Sound intensity is a measure of the power carried by sound waves per unit area. It quantifies how much sound energy passes through a specific area over a specified time. The intensity of sound is typically measured in watts per square meter (W/m²). In essence, sound intensity reflects how loud a sound is; higher intensity values correspond to louder sounds.

Sound exposure refers to the amount of sound energy that an environment or an individual is subjected to over a specific period. It is commonly measured in decibels (dB) and takes into account both the intensity of the sound and the duration of exposure. Sound exposure is an important concept in fields such as acoustics, environmental science, and audiology because it helps assess the potential impact of sound on human health, wildlife, and ecosystems.