A measure of the relative ease with which a porous medium can transmit a fluid under a potential gradient and is a property of the medium alone (after Lohman and others, 1972). The property of a porou
s medium itself that expresses the ease with which gases, liquids, or other substances can pass through it.
A variable star whose fluctuations in brightness are due to natural changes in the luminosity of the star itself, not by external causes, such as in extrinsic variable stars.
Beneath the surface magma tends to cool slowly which allows for the growth of large crystals within the rock. Rocks formed in this way are intrusive or plutonic rocks. [Wikipedia]