n. — abbreviation, Politics
the Prime Minister's Office.
Type: 5. Frequency — PMO is overwhelmingly most prevalent in Canada (see Chart 1). The term does not appear to be a preservation from the British parliamentary tradition and therefore appears to be Canadian in origin. Although PMO is often used in the news media, and by individuals connected to the Prime Minister's Office (see the 1969 quotation), it rarely occurs in the everyday speech of those who do not take a profound interested in domestic politics.
See also COD-2, s.v. "PMO", which is marked "Cdn".
Images:

Chart 1: Internet Domain Search, 11 Jul. 2013