The zeroth law of thermodynamics describes the state where we can say what about the movement of heat between two substances?

Explanation:

The zeroth law of thermodynamics is a common sense statement, which is used to define the thermal equilirium.

The zeroth law states that if a system (a substance for example) has the same temperature as a second system, and the second system has the same temperature as a third system, then the first and the third systems also have the same temperature, and, hence, they are in thermal equilibrium.

Remember that heat flows in virtue of the temperature differences, from a higher temperature substance to a lower temperature substance, so if two or more substances have the same temperature they are in thermal equilibrium, which means that there is not movement of heat between the substances.