The term
differential is used in
calculus to refer to an
infinitesimal (infinitely small) change in some
varying quantity. For example, if
x is a
variable, then a change in the value of
x is often denoted Δ
x (pronounced
delta x). The differential d
x represents an infinitely small change in the variable
x. The idea of an infinitely small or infinitely slow change is extremely useful intuitively, and there are a number of ways to make the notion mathematically precise.