This article is from the Puzzles FAQ, by Chris Cole firstname.lastname@example.org and Matthew Daly email@example.com with numerous contributions by others.
A facet of rec.puzzles culture that comes from the early days of
Usenet is based on the notion that all posts should contain either the
statement, solution, or specific commentary about puzzles. In those
nearly-forgotten days, if you wished to make a generally off-topic post,
you would include an "Obligatory Puzzle" (or ObPuzzle, for short) to amend
for whatever else you were writing about. The practice of posting
ObPuzzles continues, although the necessity for it has disappeared to the
point that posting a frequently-seen puzzle as an ObPuzzle would be
considered more rude than making a simple off-topic post.