Octahydrate refers to a chemical compound that contains eight water molecules (H₂O) for each formula unit of the substance. This term is often used in the context of hydrates, which are compounds that include water in their crystalline structure. The presence of water can significantly affect the properties of the compound, such as its solubility and stability. Common examples of octahydrates include certain salts, like copper(II) sulfate octahydrate, which is known for its vibrant blue color. These hydrates are important in various fields, including chemistry and materials science, as they can influence reactions and the behavior of substances in different environments.