1) General: A → dimensionless number characterizing
a porous medium, expressed by the ratio of the volume occupied by the pores to
the total volume of the medium.
2) Geology: The percentage volume of hollow spaces in a rock, sediment, or soil.
3) Dust grains: The quantity usually defined as:
P = (Vv/Vt) = (1 -
Vv and Vs are the volumes of vacuum
and of the solid matter making up the particle, and
Vt is the total
volume of the particle within some defined surface.
→ porous; → -ity.