What is the term for the spaces between large materials such as gravel?

The term that describes the spaces between large materials such as gravel is "porous." This characteristic signifies that the material has voids or interstices that can facilitate the movement of fluids, such as water, through it.

In the context of gravel, which is commonly used in drainage and filtration applications, the porosity is significant because it allows for the passage and retention of water, making it effective for various engineering and environmental purposes. When discussing gravel, understanding porosity helps in assessing its suitability for applications like stormwater management or aquifer recharge.

The other terms, while related to water movement and retention, don't specifically refer to the spaces within the material itself. "Pervious" indicates the ability of a material to allow water to pass through, but it does not emphasize the presence of spaces. "Saturated" refers to a condition where all voids in a material are filled with water, while "impermeable" describes materials that do not allow water to flow through them, which is the opposite of what is being asked in this question.