Water of hydration refers to the water molecules that are bound to salts or crystals in a crystalline form. It is also referred to as water of crystallization. Other synonyms for water of hydration include hydrated water, crystal water, constitutional water, and aquo. The term constitutional water is used mainly in biology, while aquo is commonly used in chemistry. These synonyms are all interchangeable in describing the water molecules that are part of the crystalline structure of a substance. Water of hydration plays an important role in various chemical and physical processes, including solubility and crystal formation. Understanding these synonyms will improve comprehension of related scientific literature and research.