Electrical conductivity is a measure of how well a material accommodates the transport of electric charge. Conductance is an electrical phenomenon where a material contains movable particles of electricity. When a difference of electrical potential is placed across a conductor, its movable charges flow, and an electric current appears.
A conductor such as a metal has high conductivity, and an insulator like glass, or the vacuum, has low conductivity. A semiconductor has a conductivity that may vary with conditions, such as exposure of the material to certain frequencies of light.
Electrical conductivity is the reciprocal of electrical resistivity (ohms). Its SI derived unit is the siemens (named after Werner von Siemens) per meter (A2s3m-3kg-1). It is the ratio of the current density to the electric field strength. This applies also to the electrolytic conductivity of a fluid.
For a discussion of the physical origin of electrical conductivity, see electrical conduction.