Porosity is a measure of the void spaces in a material, expressed as a fraction of the total volume. In the context of Earth Space Science and geology, porosity typically refers to the amount of empty space (pores) within a rock or sediment that can hold fluids, such as water or oil. It is calculated using the formula:
\[ \text{Porosity} (\phi) = \frac{\text{Volume of voids}}{\text{Total volume}} \]
Porosity is usually expressed as a percentage. High porosity indicates that a material can hold a significant amount of fluid, while low porosity means that it holds little fluid. This property is essential for understanding groundwater movement, hydrocarbon reservoirs, and the storage capacity of various geological formations.