Hydrates refer to compounds containing water molecules, which are typically used in chemistry. They play a significant role in many chemical reactions, and hence, are extensively studied. Some common synonyms for the word hydrates are aqua compounds, water of crystallization, and water complexes. Aqua compounds are substances or compounds containing water molecules that are usually bonded to metal ions. Water of crystallization is water molecular forms, frequently in solid-state, that gets trapped within crystals. A water complex is a type of chemical bond consisting of one or more water molecules bound to a central metal ion. These synonyms are essential when describing chemical reactions that involve hydrates.