A hole or cavity.

A pore is a hole or cavity. The size can determine a filter’s ability to filter our certain sizes of particles.
The pore size distribution is the comparative opulence of every pore size in an illustrative volume of soil. To represent this a function f(r) can be used, which can be compared to the mutual volume of all pores who have effective radii with an infinitesimal range centred on r.
Pore volume is the proportion of a porous material’s air volume compared to a material’s porous full volume. The full volume of a part can be defined as the space contained in a non-existent film that is tightly shrunk around the exterior geometry.