The mathematical framework combining space and time is spacetime. In modern physics, spacetime is treated as a four-dimensional continuum: three dimensions of space plus one dimension of time.
The idea emerged from special relativity, which showed that measurements of distance and duration depend on an observer's motion. In 1908, mathematician Hermann Minkowski gave Einstein's theory a geometric interpretation, demonstrating that space and time are not completely separate. A single point in spacetime is called an event and is identified by its location and time.
Spacetime also provides a way to describe motion. The sequence of events traced by a moving object forms its world line, while the spacetime interval between events remains consistent for all inertial observers even when they disagree about the separate distances and times.
In special relativity, spacetime is flat and is called Minkowski spacetime. General relativity extends the framework by allowing spacetime to curve in response to matter and energy. A common mix-up is to confuse spacetime with a spacetime diagram: spacetime is the physical-mathematical model, while a diagram is only a visual tool for representing it.