/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]