Calibration - Checking and/or adjusting an instrument such that its readings agree with a standard. Calibration removes instrument systematic error and quantifies the instrument random error.

Calibration Check - A routine check of an instrument against a reference to ensure that the instrument has not deviated from calibration since its last use.

Calibration Accuracy - The accuracy, to which a calibration is performed, usually based on the accuracy and sensitivity of the instruments and references used in the calibration.

Calibration Source, Infrared - A blackbody or other target of known temperature and effective emissivity used as a calibration reference.

Capacitance, Thermal - This term is used to describe heat capacity in terms of an electrical analog, where loss of heat in analogous to loss of charge on a capacitor. Structures with high thermal capacitance lose heat more slowly than those structures with low thermal capacitance.

Capacity, Heat - The heat capacity of a material or structure describes its ability to store heat. It is the product of the specific heat (c­­­p) and the density (r) of the material. This means that denser materials generally will have higher heat capacities than porous materials.

Celsius [Centigrade] - A temperature scale based on 0°C as the freezing point of water and 100°C as the boiling point of water at standard atmospheric pressure; a relative scale related to the Kelvin scale [0°C = 273.12 K. 1 C° (DT) = 1 K. (DT)]

Color - A term sometimes used to define wavelength or spectral interval, as in two-color radiometry (meaning a method that measures in two spectral intervals); also used conventionally (visual color) as a means of displaying a thermal image, as in color thermogram.

Colored Body - See non-graybody.

Conductance, Thermal - A measure of the ability of a material of defined thickness and cross-sectional area to conduct heat. Related to the material property, thermal conductivity. The inversed of thermal resistance (C = 1/R).

Conduction, Thermal - The only mode of heat flow in solids, but can also take place in liquids and gases. It occurs as the result of atomic vibrations (in solids) and molecular collisions (in liquids and gases) whereby energy is transferred from locations of higher temperature to locations of lower temperature.

Conductivity, Thermal,  [K] - A material property defining the relative capability to carry heat by conduction in a static temperature gradient. Conductivity varies slightly with temperature in solids and liquids and with temperature and pressure in gases. It is high for metals (copper has a K of 380 W/m-°C) and low for porous materials (concrete has a K of 1.0) and gases.

Convection - The form of heat transfer that takes place in a moving medium and is almost always associated with transfer between a solid (surface) and a moving fluid (such as air), whereby energy in transferred from higher temperature sites to lower temperature sites.