Space-time is a concept in physics that combines the three dimensions of space with the fourth dimension of time into a single four-dimensional continuum. This means that instead of thinking of space and time as separate entities, they are interwoven, affecting each other. For example, the presence of mass can warp space-time, leading to the phenomenon of gravity. In Einstein's theory of relativity, space-time helps explain how objects move and interact in the universe. When massive objects, like planets or stars, are present, they create curves in space-time, which influences the motion of other objects nearby. This understanding has transformed our view of the universe and how it operates.