Thermal conductivity is the degree of heat flux to be transferred along temperature gradient when there is a difference in unit temperature per unit length of an object. The unit is [W/(m・K)].
This means that an object with high thermal conductivity conveys heat (heat conduction) more than another object with low thermal conductivity.
There is a correlation between thermal conductivity and electrical conductivity. In general, thermal conductivity of metal is higher than non-metal. In most cases, thermal conductivity of an object is the highest in solid state, then liquid, and the lowest in gas state.