The Golden Triangle is one of Asia's two main illicit opium-producing areas. It is an area of around 367,000 square miles (950,000 km²) that overlaps the mountains of four countries of Southeast Asia: Burma, Vietnam, Laos and Thailand. Along with Afghanistan and Pakistan in the Golden Crescent, it has been one of the most extensive opium-producing areas of Asia and of the world since the 1920s. Most of the world's heroin came from the Golden Triangle until the early 21st century when Afghanistan became the world's largest producer.
The Golden Triangle also designates the confluence of the Ruak River and the Mekong river, since the term has been appropriated by the Thai tourist industry to describe the nearby border tripoint of Thailand, Laos and Myanmar.
Information based on http://en.wikipedia.org/wiki/Golden_Triangle_%28Southeast_Asia%29