In the natural sciences, including physiology and engineering, a specific quantity generally refers to an intensive quantity per unit mass, obtained by dividing an extensive quantity of interest by mass; in this case, it is also known as a mass-specific quantity. 
For example, specific leaf area is leaf area divided by leaf mass.
Derived SI units involve reciprocal kilogram (kg-1), e.g., square metre per kilogram (m2kg−1).

Another kind of specific quantity, termed named specific quantity, is a generalization of the original concept. The divisor quantity is not restricted to mass, and name of the divisor is usually placed before "specific" in the full term (e.g., "volume-specific storage" or "thrust-specific fuel consumption"). 

Named and unnamed specific quantities are given for the terms below.

List

Mass-specific quantities
Per unit of mass (short form of mass-specific):
 Specific absorption rate, power absorbed per unit mass of tissue at a given frequency
 Specific activity, radioactivity in becquerels per unit mass
 Specific energy, defined as energy per unit mass
 Specific internal energy, internal energy per unit mass
 Specific kinetic energy, kinetic energy of an object per unit of mass
 Specific enthalpy, enthalpy per unit mass
 Specific enzyme activity, activity per milligram of total protein
 Specific force, defined as the non-gravitational force per unit mass
 Specific growth rate, increase in cell mass per unit cell mass per unit time
 Specific heat capacity, heat capacity per unit mass, unless another unit is named, such as mole-specific heat capacity, or volume-specific heat capacity
 Specific latent heat, latent heat per unit mass
 Specific leaf area, leaf area per unit dry leaf mass
 Specific modulus, a materials property consisting of the elastic modulus per mass density of a material
 Specific orbital energy, orbital energy per unit mass
 Specific power, per unit of mass (or volume or area)
 Specific relative angular momentum, of two orbiting bodies is angular momentum per unit reduced mass, or the vector product of the relative position and the relative velocity
 Specific surface area, per unit of mass, volume, or cross-sectional area
 Specific volume, volume per unit mass, i.e. the reciprocal of density

Other specific quantities
Per unit of other types. The dividing unit is sometimes added before the term "specific", and sometimes omitted.
 Brake-specific fuel consumption, fuel consumption per unit of braking power
 Thrust-specific fuel consumption, fuel consumption per unit of thrust
 Specific acid catalysis, in which the reaction rate is proportional to the concentration of the protonated solvent molecules
 Specific acoustic impedance, ratio of sound pressure p to particle speed at a single frequency
 Specific capacity of a water well, quantity of water produced per (length) unit of drawdown
 Specific conductance, conductance per meter. Identical to electrical conductivity
 Specific detectivity of a photodetector
 Specific fuel consumption (disambiguation). Fuel consumption per unit thrust, or per unit power. Type defined as above.
 Specific gas constant, per molar mass
 Specific gravity, relative density in comparison with water (ratio of density per water density) (mass per unit volume, in CGS or equivalent units.)
 Specific heat of vaporization, enthalpy of vaporization, vaporizing heat per mole
 Specific humidity, mass of water vapor per unit mass dry air
 Specific impulse, impulse (momentum change) per unit of propellant (either per unit of propellant mass, or per unit of propellant by Earth-weight)
 Specific mass, actually meaning volume-specific mass, or mass per unit volume. Same as density.
 Specific melting heat, enthalpy of fusion; melting heat per mole
 Specific modulus, elastic modulus per mass density
 Specific resistance (disambiguation), several scientific meanings
 Specific rotation of a chemical, angle of optical rotation α of plane-polarized light per standard sample with a path length of one decimeter and a sample concentration of one gram per millilitre
 Specific speed, unitless figure of merit used to classify pump impellers (pump-specific) and turbines (turbine-specific). Ratio of performance against reference pump that needs one unit of speed to pump one unit volume per one unit hydraulic head pressure. For a turbine, it is performance measured against a reference turbine that develops one unit of power per one unit speed per one unit of hydraulic head.
 Specific storage, specific yield, and specific capacity, quantify the capacity of an aquifer to release groundwater from storage per unit decline in hydraulic head pressure
 Specific strength, material strength (pressure required at failure) per unit material density
 Specific surface area, per unit of mass, volume, or cross-sectional area
 Specific surface energy, free energy per unit surface area
 Specific thrust, thrust per unit air intake rate
 Specific weight, weight per unit volume

Usage

Reference tables Specific properties are often used in reference tables as a means of recording material data in a manner that is independent of size or mass. This allows the data to be broadly applied while keeping the table compact.

Ranking, classifying, and comparing Specific properties are useful for making comparisons about one attribute while cancelling out the effect of variations in another attribute. For instance, steel alloys are typically stronger than aluminum alloys but are also much denser. Greater strength allows less metal to be used, which makes the choice between the two metals less than obvious.  To simplify the comparison, one would compare the specific strength (strength to weight ratio) of the two metals. A more everyday example relates to grocery shopping: a 2 kg package sells for a higher price than 1 kg package of the same foodstuff, but what matters is the "specific price", commonly called the unit cost (cost in currency units per kilogram).

Mnemonics and qualitative reasoning In many instances, specific properties are more intuitive or are easier to remember than the original properties, whether in SI or imperial units. For instance, it is easier to conceptualize an acceleration of 2g than an acceleration of 19.6 meters per second squared.

See also
Intensive_and_extensive_properties#Specific_properties

References 

Physical quantities