- (economics) A market situation in which two companies exclusively provide a particular product or service.
- (by extension) The domination of a field of endeavor by two people or entities.
- 2012 June 29, Kevin Mitchell, “Roger Federer back from Wimbledon 2012 brink to beat Julien Benneteau”, in The Guardian, archived from the original on 15 November 2016:
- In 2011, his spirit and body were shattered by Jo-Wilfried Tsonga in the semi-finals. Last night, the stakes were just as high – even though the tournament is not out of the first week – because there is a creeping perception that the [Roger] Federer–[Rafael] Nadal duopoly is slowly giving way under pressure from below.
- (broadcasting, by extension) Situation in which two or more TV or radio-stations in the same city or community share common ownership.
market situation in which two companies exclusively provide a particular product or service