As CPW says, it's in relation to where on your body. So, yes, belly button would be 12 o'clock, small of the back 6 o'clock.
I carry with the gun at 6 o'clock (or very close, slightly offset toward 7 o'clock because I have long arms, so it's more comfortable to reach ever so slightly further,) with the muzzle pointed (if you were looking at me from behind,) down and to the left, grip-up. (So that when I draw - right-handed - the muzzle naturally swings down along my right side before I pull it up.) With my weapon, this position is fully concealed VERY easily, even with a moderately tight over-shirt tucked in. (Although that makes it much harder to draw, so I usually go untucked.)
When I'm not at a range with an "action range" that allows draw-and-fire practice, I usually practice with my son's airsoft pistol. It's bigger (fake M1911,) but if anything, that makes sure I practice clearing it better.