What is defined as the volume occupied by pore spaces or voids in the rock?

The term that refers to the volume occupied by pore spaces or voids in the rock is porosity. Porosity is a crucial property in geology and hydrogeology as it quantifies how much space is available within a rock or sediment for fluids like water, oil, or gas. The higher the porosity of a material, the greater the volume of voids, allowing more fluid to be stored.

For instance, in the context of aquifers, which are geological formations that can store and transmit water, porosity plays an essential role in determining their capacity to hold water. If a rock has low porosity, it will contain less water, affecting the overall availability of groundwater.

Permeability, while related to porosity, describes the ability of a material to allow fluids to flow through its pore spaces, rather than the volume of those spaces themselves. The water table refers to the upper surface of the saturated zone in an aquifer, establishing the boundary between the water-saturated ground and the unsaturated ground above. Thus, porosity is specifically about the space within the rock, making it the correct answer.