A differential, often referred to as a difference, is a mathematical concept that represents the change in a quantity. In calculus, it describes how a function changes as its input changes. For example, if you have a function f(x), the differential df indicates how much f changes when x changes by a small amount dx. In everyday terms, the differential can be thought of as the slope of a curve at a specific point. It helps in understanding rates of change, such as speed or growth. This concept is widely used in various fields, including physics, engineering, and economics, to analyze dynamic systems.