And the word goes round
In the old days, when everybody was a "man" and copy editors still worked with pencils and paper, copy desks were often horseshoe-shaped. Rank-and-file editors -- "rim men" -- sat around the outside, while the guy in charge sat in the "slot" so he could reach all the rim guys when he needed to hand out stories to work on.
The term is still widely used today (though often it's just "slot"), and some copy desks are still set up in basically the same fashion, except with computers.
That's from The Slot, the greatest blog for word nerds and anyone else who cares about the proper placement of apostrophes and the correct usage of "round" and "till." (No apostrophes needed for those.)
Check out the Slot Man. Good stuff. And helpful when you have a quirky usage question.