Thermal conductivity is the ability of a material to conduct heat. Metals are good at moving heat. They are good conductors of heat. Gases are also good at moving heat. They are also good conductors of heat. Thermal resistivity is the opposite of thermal conductivity.
Thermal conductivity is often represented by the Greek letter "kappa", . The units of thermal conductivity are watts per meter-kelvin. Watts are a measure of power, meters are a measure of length, and kelvins are a measure of temperature. From the units, we can see that thermal conductivity is a measure of how much power (in watts) moves through a distance (in meters) due to a temperature difference (in kelvin).