A Partial Differential Equation (PDE) is a type of mathematical equation that involves multiple variables and their partial derivatives. Unlike ordinary differential equations, which deal with functions of a single variable, PDEs are used to describe phenomena where changes occur in more than one dimension, such as in physics, engineering, and finance. For example, they can model how heat spreads through a material or how waves propagate in water. PDEs are essential in fields like fluid dynamics, quantum mechanics, and electromagnetism. Solving these equations often requires advanced techniques and numerical methods, as they can be quite complex. Understanding PDEs helps scientists and engineers predict and analyze real-world behaviors in various systems.