The Fourth Dimension
A dimension is a measurement used to describe an object or a point in space.  All dimensions are arbitrary notions. A line is measured in one dimension because only one coordinate is needed to specify a point on it or to determine its length (which is a series of points). A surface such as a plane or surface is measured with two dimensions because two coordinates are needed to specify a point on it or determine its area. A  cube, a cylinder or a sphere is tri-dimensional because three coordinates are needed to locate a point within this spaces, or to determine its volume.

An object in motion is measured with four dimensions because four coordinates are needed to locate it space/time (reality).

There is a common misconception people are confused by the term "fourth dimension" because science fiction has led them to believe that time is something that actually exists as a location.  This is incorrect, because there is no evidence that time actually exists outside of the confines of the human mind. When we measure time we are actually measuring motion, such as the movement of the hands of a clock.

The fourth dimension is used to describe the motion and rate of motion of an object. All dimensions are notions in the mind of man. Or as Dr. Albert Einstein once said ,
us physicists believe the separation between past, present, and future is only an illusion, although a convincing one”.

Marcus Aurelius wrote, “Time is like a river made up of the events which happen, and a violent stream; for as soon as a thing has been seen, it is carried away, and another comes in its place, and this will be carried away too.”

We may imagine time as a flowing stream of water and reality is the flotsam and jetsam flowing within it.
A small object floating in a stream only affect other objects by coming in contact with them. To float upstream (go back in time) would require more energy than anything in the stream possesses, though it is possible for various items in the stream to be propelled ahead of other items (travel into the future.