Hi!
It's not entirely correct to say that there are 4 "known" dimensions. Time is the "4th" dimension only when applied to space-time theories. What we actually have, are 3 spatial dimensions plus 1 time dimension.
In string theory (or more specifically, M-theory), there are 11 dimensions (10 spatial dimensions and one time dimension).
What the 5th dimension would be therefore depends on what theory you are talking about.
Check out our hypography on
Hyperspace.
You should also search our website for the word dimensions, it will give you lots of relevant pages.
Tormod
