Swelling is the increase in volume of a gel or solid associated with the uptake of a liquid or gas.
Imbibition is the uptake of a liquid by a gel or porous substance. It may or may not be accompanied by swelling.
Syneresis is the spontaneous shrinking of a gel with exudation of liquid.
Swelling pressure ( sw or ) is that pressure difference which has to be established between a gel and its equilibrium liquid, to prevent further swelling of the gel.
Colloid osmotic pressure (Donnan pressure) ( or ) is the pressure difference which has to be established between a colloidal system and its equilibrium liquid to prevent material transfer between the two phases when they are separated by a membrane, permeable to all components of the system, except the colloidal ones.
Reduced osmotic pressure is the osmotic pressure divided by mass concentration.