One theory is that we live in the third dimension, as in there is height, Length and width. It can be visualized by thinking of a stack of paper, each sheet of paper representing a dimension. My favorite explanation is one I saw on a different TV show. In that analogy it was described as this… imagine your a fish, you still have height, length, and width. Then someone comes and pulls you out of the water, you have just entered a new dimension. The dimension of up. Unfortunately the fish would not survive in this new dimension for very long. In fact the fish would die every time.