Differentials are mathematical tools used to describe how a function changes as its input changes. They help in understanding the rate of change of a function at a specific point. In calculus, the differential of a function provides a way to approximate the change in the function's value when the input changes slightly. In practical applications, differentials are used in various fields, including physics and engineering, to model real-world phenomena. For example, they can help calculate the slope of a curve or determine how small changes in variables, like time or temperature, affect outcomes in systems described by differential equations.