Why clay is called impervious?

Clay is often referred to as "impervious" because it has very low permeability, meaning it does not allow water or other fluids to pass through easily. This characteristic is due to its fine particle size and compact structure, which create minimal spaces for fluid movement. As a result, clay can effectively act as a barrier to water, making it suitable for applications like liners in landfills and ponds. Additionally, its impervious nature helps in retaining moisture in soil, benefiting agricultural practices.