A partial derivative of a function of several variables is its derivative with respect to one of those variables, with the others held constant. It is used in vector calculus and differential geometry. The partial derivative of a function with respect to a variable is denoted by symbols such as ∂f/∂x or fx. It can be thought of as the rate of change of the function in a specific direction. For example, if we have a function f(x, y) depending on two variables x and y, then the partial derivative of f with respect to x, taking y as a constant, is denoted as ∂f/∂x. Similarly, the partial derivative with respect to y, taking x as a constant, is denoted as ∂f/∂y. The process of finding the partial derivatives of a given function is called partial differentiation. It is used to find the slope in a specific direction and is essential in various fields of mathematics and science, including physics, engineering, and economics.