Your
physics teachers have been lying to you.
All throughout the day we are engaged in motion through space. We move forward. We move backward. We do the
lambada.
But, to understand the fundamental structure of motion, we must also consider motion with regard to time. This dimension -- motion with regard to time -- is the fourth dimension. A quick
example, if I may.
A man may reside on 10th street, on 6th avenue, on the third floor of the I_B Hotel.
Now, if one was to meet that man at 1:00 A.M at his room, their fixed position would be: (10 Street, 6th Avenue, 3rd Floor).
Also important is the
time that person was at the
hotel, which would be the forth piece of information, which would be 1:00 A.M.
See
The fourth dimension (no, really) for an unabridged version.