Other contributors have said "Is clay a porous rock?" is the same question as "What rocks are porous?" If you believe that these are not asking the same thing and should be answered differently, click here
Porosity or void fraction is a measure of the void (i.e., "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0--1, or as a percentagebetween...
one which allows water to seep between the gaps between the grains which make up the rock. This is because the grains are non-interlocking therefore water can get through. You can look at it a bit...