In the science of physics, spacetime is a mathematical model that combines space and time into a single construct called the spacetime continuum. Spacetime is usually interpreted with space being three-dimensional and time playing the role of a fourth dimension that is of a different sort than the spatial dimensions.
The concept of spacetime combines space and time within a single coordinate system, typically with three spatial dimensions: length, width, height, and one temporal dimension: time. Dimensions are components of a coordinate grid typically used to locate a point in a certain defined "space" as, for example, on the globe by latitude and longitude. In spacetime, a coordinate grid that spans the 3+1 dimensions locates "events", so time is added as another dimension to the grid.
According to certain Euclidean space perceptions, the universe has three dimensions of space and one dimension of time. By combining space and time into a single manifold, scientists have significantly simplified a large number of physical theories, as well as described in a more uniform way the workings of the universe at both the supergalactic and subatomic levels.
In classical mechanics, the use of Euclidean space instead of spacetime is appropriate, as time is treated as universal and constant, being independent of the state of motion of an observer. In relativistic contexts, however, time cannot be separated from the three dimensions of space, because the rate at which time passes depends on an object's velocity relative to the speed of light and also on the strength of intense gravitational fields which can slow the passage of time.