Lorentzian Geometry is a mathematical framework used to describe the geometric properties of spacetime in the theory of relativity. It extends the concepts of traditional geometry to account for the effects of time and the speed of light, allowing for a unified treatment of space and time. In Lorentzian Geometry, the metric used to measure distances is not positive-definite, which means it can account for the differences between time-like, space-like, and light-like intervals. This structure is essential for understanding how objects move and interact in the universe, particularly in the context of Einstein's theory of relativity.