A parametric equation is a way to express a mathematical relationship using one or more parameters. Instead of defining a curve or surface with a single equation, parametric equations use variables, often denoted as t, to describe the coordinates of points. For example, a circle can be represented with equations for x and y in terms of t, allowing for a more flexible representation of shapes. These equations are particularly useful in fields like physics and engineering, where they can describe motion and trajectories. By varying the parameter, you can trace out a path or surface, making it easier to analyze complex shapes and movements compared to traditional Cartesian equations.