A Partial Derivative is a derivative where we hold some variables constant while differentiating with respect to others. This concept is essential in multivariable calculus, allowing us to analyze functions of several variables by focusing on how they change in relation to one variable at a time. For example, in a function of two variables, such as f(x, y), the partial derivative with respect to x measures how f changes as x varies, while keeping y fixed. This technique is crucial in fields like physics and engineering, where systems often depend on multiple factors.