/ob/ prefix ObligatORy. A piece of netiquette acknowledging that the authOR has been straying from the newsgroup' s charter topic. FOR example, if a posting in alt.sex is a response to a part of someone else' s posting that has nothing particularly to do with sex, the authOR may append "ObSex" (OR "Obsex") and toss off a question OR vignette about some unusual erotic act. It is considered a sign of great winnitude when one' s Obs are mORe interesting than other people' s whole postings. [Jargon File]