Introduction:
In the field of thermodynamics, a system refers to the portion of the universe that is under consideration. A system can have various properties that describe its behavior and characteristics. These properties can be classified into two categories: extensive properties and intensive properties. Extensive properties depend on the size or amount of the system, while intensive properties do not.

Explanation:
Out of the given options, heat (option D) is not a property of the system. Let's understand why this is the case.

Properties of the system:
1. Pressure:
Pressure is defined as the force exerted per unit area. It is an intensive property that describes the distribution of force over an area. Pressure can be measured and calculated at a specific point within the system, and it can vary from one point to another. Therefore, pressure is a property of the system.

2. Temperature:
Temperature is a measure of the average kinetic energy of the particles within a system. It is an intensive property that does not depend on the size or amount of the system. Temperature can be measured at a specific point within the system, and it can vary from one point to another. Therefore, temperature is a property of the system.

3. Density:
Density is defined as the mass per unit volume of a substance. It is an intensive property that describes how tightly packed the particles are within a system. Density can be measured at a specific point within the system, and it can vary from one point to another. Therefore, density is a property of the system.

Heat as a transfer of energy:
Heat, on the other hand, is not a property of the system but rather a form of energy transfer. Heat is the transfer of thermal energy between two systems or between a system and its surroundings due to a temperature difference. It is not an inherent property of the system itself, but rather the result of energy transfer. Therefore, heat is not a property of the system.

Conclusion:
In summary, pressure, temperature, and density are properties of the system, while heat is not. Heat is a form of energy transfer, and although it can affect the properties of a system, it is not an inherent property of the system itself.