Conductivity and Resistivity
Conductivity is the degree to which a specified material conducts electricity, calculated as the ratio of the current density in the material to the electric field that causes the flow of current. Resistivity is the reciprocal of conductivity, and so are interchangeable as long as one tracks the inversions (and, correspondingly, the units). Electrical conductivity tells us how well a material will allow electricity to travel through it, and is similar to thermal conductivity, which tells us the ease upon which thermal energy (heat for most purposes) can move through the material[1].
A conductor is a material which gives very little resistance to the flow of an electric current. Correspondingly, an insulator is a material which is very resistant to the flow of electric current. Semiconductors are materials which display the properties of both conductors and insulators. The most common example of conductive materials are metals, while insulators include materials such as wood or plastics [2]. Semiconductors are generally more rare, but are necessary for the construction of transistors, and as such are present in all computers, with the most common being doped silicon[3]. In addition to these categories, there are superconductors, which have zero resistance under certain conditions (generally extremely low temperatures and/or extremely high pressures)[4], as well as a host of other materials with odd behaviors.
The units for conductivity and resistivity are most naturally expressed in terms of the recognizable Ohm ([math]\displaystyle{ \Omega }[/math]). Resistivity has units of [math]\displaystyle{ \Omega \cdot m }[/math], so conductivity has units of [math]\displaystyle{ \frac{1}{\Omega \cdot m} }[/math]. Expressed in terms of SI base units, the unit of resistivity becomes [math]\displaystyle{ \frac{kg\cdot m^3}{s^3\cdot A^2} = \frac{kg\cdot m^3}{s\cdot C^2} }[/math].