Do you know the real definition of MCPCB thermal conductivity?

Do you know the real definition of MCPCB thermal conductivity?
There were many MCPCB guys don’t know the MCPCB thermal conductivity.
Special some new comer have no idea about it.
So Allen wants to discuss this topic.
First of all I want to claim not a decades MCPCB expert discuss with you, if you have any question or I have had mistakes, please let me know and I will correct them.

Here the detail number you may didn’t remember, but you must know the thermal conductivity is a very important parameter.
It is directly proportional to the thermal conductivity of the base material.
i.e. ~135W/m.k in case of Aluminum and ~385W/m.k in case of copper.
Most designs use Aluminum PCB metal as a base material.
Do you know the real definition of MCPCB thermal conductivity?