A porous medium refers to any material that is permeable and allows fluids to pass through it. There are various synonyms used to describe a porous medium, such as a permeable substrate, a porous material, a porous matrix, or a fluid-containing rock. Another common synonym is a permeable soil, which refers to soil that allows water to move through it easily. A spongy matrix is another synonym used to describe a material that is highly porous and can absorb large amounts of liquid. Other synonyms used include a permeable membrane, a porous filter, and a porous fabric. Overall, these synonyms are used interchangeably to refer to any material that has a high level of porosity, allowing fluids to pass through it with ease.