The gap between a pair of adjacent railway tracks, where they are running in oppositedirections. The actual distance can be anything up to twelve feet depending how fast the trains run, but it's always called a sixfoot.
Standing in the sixfoot is like standing on the lane-marker of a road; you shouldn't get hit when a train passes, but you'll be really close.
We were working in the sixfoot when the ballast gave way under us and I fell into the fourfoot - good job my mate pulled me clear before the train came.
You might find this used on web chatting programs or internet message boards:
Sixfootpolecat99: "Hey, how's it going everyone"
Randomperson1:"Not bad"
Randomslut_01:"pretty good, f/19/VA/horny here, how about you?"
Sixfootpolecat_11: "Hi Sixfootpolecat99, want to meet and have buttsex?"
Sixfootpolecat99: "Sweet, I'll catch!"