This term is not in
common usage, but you might hear it if you spend enough time talking with hardcore
science fiction fans. It requires a rather complex
hypothetical situation to define. If you disagree with any of the premises below completely you may feel the term is meaningless, but the basic idea remains if you just
adjust the numbers up or down. If you get bored
skip this node, it probably won't have much impact on your life.
(A) Suppose there is one chance in a thousand that we will encounter an alien civilization one way or another in the next forty or fifty years.
(B) Suppose that a certain science fiction book does such a good idea job of loosening our preconceptions about aliens and helping us to think rationally about understanding them and is so well written that there is one chance in a thousand that good ideas from that book will diffuse through our culture and have a significant positive impact on any first contact. (We're assuming a really great book might be widely read though a period of forty or fifty years).
Suppose something having a significant positive impact on a first contact with aliens might save a million lives, either by helping us bargain for a cure for cancer or avert a war or shorten a war or whatever.
Given these assumptions, there is one chance in a million that both A and B might happen as a result of the writing of any superb first contact book. There could well be more than one such book, with each having an independent one chance in a thousand.
If A and B did both happen for any given book, the net result would be to save a million lives or more. The net positive impact of a book having one chance in a million of saving a million lives. The writing of such a book has an expected statistical average effect of saving one life. The writing of such a book would, so the theory goes, be the moral equal of saving a life.
There is no physical or agreed on 'club' - just a people can debate endlessly which books are truly great, so certain fans could debate endlessly on which books are members of the thousandth thousand club. Of course it should be a set rather than a club, since books rather than people are members and there is no set roster, but I've never heard the term used any other way. I've never met anyone fanatical enough to deny the numbers are all arbitrary, even if they agree with the basic idea. Even more speculative is the related idea of the negative club.