Minkowski Space, defined simply and quickly, is a name for the fourth dimensional
space in which our
universe resides. This concept was used by
Albert Einstein in his paper
Relativity: The Special and General Theory, and was central to his core argument. Einstein said, "Without it (Minkowski's work) the general theory of relativity, of which the fundamental ideas are developed in the following pages, would perhaps have got no farther than its long clothes."
We live in a three dimensional universe, in which a point can represented by coordinates (x, y, z), which is embedded in a four dimensional universe which adds a fourth coordinate, t, representing time. Now, a point can be represented as (t, x, y, z). Perhaps an hour later, whatever was in that point has moved, and something else occupies that space. However, the point is not the same; time has passed, and we now call the point (t', x, y, z). Without this fourth dimension, our lives would be like taking every frame on a movie reel and stacking them on top of each other, a huge jumble of every moment occurring at the same time, with no sequential movement. This 4-D representation of the universe is often called space-time. Einstein used this idea, in the form of the fourth equation of the Lorentz transformation, to prove that time was not independent of space.
**snip all the stuff about curved space... turns out Minkowski Space isn't curved. I've moved the description of space curved by gravity to the curved space node, minus the globe thing, since there's a great description of that sort of thing there already**
And many thanks to cjeris and Miles_Dirac for pointing out what I didn't know, and then enlightening me (and all of us).