/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]