Deliquescence
The property of a solid that absorbs enough water vapour from the air to dissolve completely in the water it takes up.
Unit
Dimensionless
In depth
Deliquescence occurs when the saturated solution of the salt has a vapour pressure lower than the ambient partial pressure of water, so absorption continues until equilibrium. It is the extreme end of hygroscopy, and it makes accurate weighing impossible unless the sample is handled in a desiccator or glove box.
Examples in the real world
Sodium hydroxide pellets turning to a syrup on the bench, and calcium chloride used as a road de-icer and drying agent.