A water mill is a type of mill that uses the energy of flowing water to grind grain into flour or to power other machinery. There are various synonyms for the term "water mill", including waterwheel mill, hydropower mill, and water-powered mill. Another synonym for water mill is a "watermill", which is simply an alternative spelling. In some regions, water mills are referred to as "tide mills" or "stream mills" depending on their location. Other synonyms include "millpond mill" and "bathtub mill". Regardless of the terminology used, these mills have played an important role in history as a source of renewable energy for centuries.