That site's a load of crap.
Spacetime has four dimensions (as Sverian indicated these days the convention is take time as the 'zeroth dimension', but it is only just a convetion and it doesn't really matter, infact rather than assigning numbers we could assign the names 'John', 'Paul', 'George' and 'Ringo' if we wanted), for any given obsrever 3 of them will be the three dimenisions of spaceas experinced by him (i.e. 'space' for some observer is a hypersurface of spacetime) and one will be his time dimensions.
I personally like to think of thing in terms of vector spaces, so a dimension to me is just the cardinality of the largest set of linearly indpendent vectors.