The expression "dx² - dy²" represents a mathematical concept often encountered in calculus and differential equations. It describes a form of a quadratic expression in two variables, where "dx" and "dy" can be thought of as small changes or differentials in the variables "x" and "y." This expression is significant in various fields, including physics and engineering, where it can represent certain types of surfaces or curves. In the context of conic sections, "dx² - dy²" can relate to hyperbolas. Hyperbolas are defined as the set of points where the difference of the distances to two fixed points (foci) is constant. This relationship is crucial in understanding the geometry of these shapes and their applications in areas such as astronomy and navigation.