The term "anhydrous" refers to a substance that does not contain any water. It is derived from the Greek words "an," which means without, and "hydro," which means water. An anhydrous substance has had all of its water removed or chemically bound up in some way so it no longer exists as a free liquid. This can occur naturally through evaporation or other processes, or it can be intentionally removed during the production process to create a more concentrated form of the substance.