Agree with bimjob - Time. An object needs length, width, depth, (3 Dimensions) and duration (4th dimension, which is Time).
Most people consider time to be the fourth dimension (space time). In order to see an object in space you have to have the proper space time.
For example: If you place a vase of flowers on a table at precisely 3:00 PM Est on Wednesday and remove it from the table 4:00 on the same day, in order to see the flowers you had to look at them between 3 and 4 pm on Wednesday. If you looked at the table before 3:00 PM EST or after 4:00 EST you would not see them because they are now in a different space time dimension.
Others consider tetraspace to be the fourth dimension and time the fifth. Here is a site that can explain it better than I ever could.
tetraspace.alkaline.orgA space elevator by 2018?
Well, this is what I learned. The faster you go towards the speed of light, the slower time goes. When you reach the speed of light, time stops. When you go past the speed of light, time goes backwards, thus you are thrown into a fourth dimension. Some say that this is the same dimension as when one is thrown into a black hole. They are thrown into nothingness, there is no color and no explanation. I don't know if this is the answer you are looking for, but as danbob and bimjob said, time can also be considered a fourth dimension. Hope this helped!!!End to space
4th dimension in einsteinian space is TIME.Space