Water of crystallisation is water that is chemically bonded into a crystal structure.
Here is the formula for hydrated copper(II) sulfate. Notice that water of crystallisation is separated from the main formula by a dot.
CuSO4.5H2O 鈫 water of crystallisation
hydrated means that the solid crystals contain water of crystallisation.
dehydration is the removal of water of crystallisation.
an anhydrous substance contains no water of crystallisation.
the degree of hydration is the number of moles of water of crystallisation chemically bonded in 1 mole of the compound. The degree of hydration in the example above is 5.