A term used to describe used books (probably new books too, but the only way to get new book club editions is through a bookclub, in which case you don't need to be told...)
Bookclub editions tend to be of poorer quality, slightly smaller, and of almost no interest to the majority of collectors. If you're selling books on-line, you should always specify if your hardbacks are bookclub or trade editions. (With paperbacks it rarely matters, and with mass-market paperbacks it never matters).
To find out if you have a bookclub edition, look at the DJ (dust jacket). if it has a price, it's trade, if it doesn't, it may very well be bookclub (It might also be price clipped, or maybe just unusual).
Next, look at the size. Bookclub hardback fiction
books tend to be around 13 1/2 X 20 3/4 CM
, or 5 1/4 X 8 1/4 Inch. Trade are most often about 15 1/2 X 23 1/2 CM, or 6 1/4 X 9 3/8 Inches.