Popular since the mid-1800s, triple sec is an orange-flavored liqueur derived from the dried peels of oranges both bitter and sweet. "Sec" is the French word for dry, but when referring to liqueurs it means distilled. Triple Sec, therefor is a triple-distilled orange liqueur.
"Our Triple Sec is a colorless, sweet liqueur," Leroux explains in its Manual on Liqueurs. "Its flavor is obtained through the careful distillation of a maceration of the Curaçao peels together with the proper complementary ingredients and other types of oranges."
The Curaçao orange is native to its namesake island in the Dutch West Indies. It evolved from Seville orange trees introduced from Spain in 1527 which did not thrive in the arid climate, producing a bitter green fruit whose dried peels are distinctively aromatic.
Triple Sec is an essential cocktail mixer for drinks like the Sidecar Cocktail, Margaritas, Cosmopolitan, and Long Island Iced Tea.
Manual on Liqueurs by Leroux. New York, NY; 1980.