fourth dimension, noun
- : a dimension in addition to length, breadth, and depth
- : something outside the range of ordinary experience
A little bit of physics, now! It is generally accepted (backed up by Einstein's relativity theory) that the fourth dimension is time. Thus, in order to confirm an exact point, you need 3 coordinates for where (length, width, depth) and 1 coordinate for when (time).
The idea of making time the fourth dimension began with Jean le Rond d'Alembert's Dimensions, published in 1754 in the Encyclopédie, ou dictionnaire raisonné des sciences, des arts et des métiers. Yes, I had to look that one up. :)








