Within the world that we live in, we know three dimensions that apply to space, which are up-down, wast-west, and north-south, which are our form of directions as in where to be, to go, and other things of that nature. However there are the Fourth and Fifth Dimension that also exist within our space.
The Fourth Dimension is considered as Time. Thou we can move freely within west, east, north, and south, along with moving up and down, we can't move within time freely but only go forward in time. Physicists experimented with spacetime and discovered that both space and time are unified in different ways. They discover that as we look out into the sky, we look backwards in time due to how long it takes for light to reach us here on Earth's surface.
The Fifth Dimension also known at the Outback, is a space that is perpendicular to our dimension or brane. In the film, it is viewed as a viewpoint into physical manifestations of time where it can be interacted with. As where Cooper was able to change some events and cause the saving of humanity by messing around with stuff in his daughter's bedroom, eventually finding out how to give her the equation to figure out gravity. The way to the fifth dimension as seen by Cooper, was that "We brought ourselves here", meaning he thinks that not in his lifetime will this be created or movable with, as we to this day are still trying to figure out time travel, so we can travel freely in time, but at the moment can only travel in 3 dimensions to this day.
However there is more than just five dimension, but the fifth dimension is actually about 6 more, but for the sake of the movie, 6 is too many, and the decided to make it only the fifth dimension.
"Before Creation, comes Destruction."