What are the numbers on copyright pages of books, such as 10 9 8 7 6 5 4 3 2 1, for?
The represent different print runs of the same edition. For each run, a number is removed.
Lots of useful info about print runs and editions here, including the answer to your question. Derleth is correct.
It’s pretty much a leftover from the days of hot type. The plates were expensive to redo for each edition, so instead of saying “First Edition,” the resetting the type for the second edition, you put the numbers.
Now, for the second edition, you’d scrape off the number 1 from the plates. No need to reset type and it could be done in a few minutes with a knife. It would now read “10 9 8 7 6 5 4 3 2”
RealityChuck, if you replaced the word “edition” with “print run” you’d be correct.
They remove a number when they do a new print run of the same edition. A new edition meant new plates, and they’d start back at 1 with the print run numbers.