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.