modus operandi; M.O. Method or way of working. Method of proceeding with a task. Characteristic manner of operation or procedure; as with a criminal who uses a unique modus operandi (M.O.) and can thus be identified because of his special way of committing his criminal activities. This phrase is not restricted to police use. It refers to any work... Found on http://www.wordinfo.info/words/index/info/view_unit/3474/4