A substance with pores is known as a porous medium or material. The skeletal portion of the substance is frequently referred to as the "matrix" or "frame." Usually, a fluid is present in the pores. The skeletal material is typically solid, but foamy structures can also be usefully analysed using the idea of porous media. The most common attribute of a porous medium is porosity. Other characteristics of the medium, such as permeability, tensile strength, electrical conductivity, and tortuosity, can occasionally be determined from the characteristics of its components (solid matrix and fluid), as well as the porosity and pore structure of the medium, but this process is typically complicated. A poroelastic medium is the only one where the concept of porosity is simple. A sponge, for example, has two interpenetrating continua made up of the solid matrix and the pore network (also known as the pore space). The pore space that is open to flow is known as effective porosity, whereas closed porosity refers to the pore space that is blocked off to flow. Many naturally occurring materials, including rocks and soil (such as aquifers and petroleum reservoirs), zeolites, biological tissues (such as bones, wood, and cork), and man-made materials, such as cement and ceramics, can be categorised as porous media. Only by assuming that they are porous medium can many of their crucial characteristics be explained.