1. The process by which a liquid, or a mixture of gases and liquid, is drawn into and tends to fill permeable pores in a porous solid material;
usually accompanied by a physical change, chemical change, or both, of the material.
2. The increase in weight of a porous solid body resulting from the penetration of liquid into its permeable pores.
3. The increase in weight of a brick or tile unit when immersed in either cold or boiling water for a stated length of time; expressed as a percentage of the weight of the dry unit.
4. The process by which radiant energy, which is incident on a surface, is converted to other forms of energy.
5. See sound absorption.
6. See light absorption.