The word "porous" refers to a material that has pores, or holes in its surface; some examples of porous materials include sponges, pumice stones and cork. Some porous materials have more noticeable pores than others, and this quality of porousness is described as a material's porosity. Human skin is porous, for example, and pores are more pronounced on some people's skin than on others.
Volcanic rocks, including pumice, tend to be porous. These rocks tend to be a good example of the fact that a porous material doesn't necessarily have holes that cut through the entire material. Some porous materials have little interconnections between pores. For example, volcanic rocks tend to be made up of hundreds of tiny pores that are only a few centimeters deep. In this sense, porous materials are rarely sieve-like. For instance, bone is a porous material, but it is also solid and strong enough to bear weight and stand up to a relatively high level of shock. Similarly, wood is considered to be porous, although its pores are not always visible to the naked eye, and it is also a strong enough material to be used in building furniture and serving as the structural foundation of a home.