A fluent is a time-varying quantity or variable.^[1] The term was used by Isaac Newton in his early calculus to describe his form of a function.^[2] The concept was introduced by Newton in 1665 and detailed in his mathematical treatise, Method of Fluxions.^[3] Newton described any variable that changed its value as a fluent – for example, the velocity of a ball thrown in the air. The derivative of a fluent is known as a fluxion, the main focus of Newton's calculus. A fluent can be found from its corresponding fluxion through integration.^[4]