Kruskal–Szekeres coordinates

Kruskal–Szekeres coordinates are a specific set of coordinates used in the context of general relativity, particularly to describe the Schwarzschild solution, which describes the spacetime surrounding a spherically symmetric, non-rotating mass such as a black hole. These coordinates are particularly useful because they allow for a smooth and complete description of the Schwarzschild black hole, including regions that might be singular or undefined in standard Schwarzschild coordinates.