Context (emphasis mine):
We Bokononists believe that humanity is organized into teams, teams that do God's Will without ever discovering what they are doing. Such a team is called a karass by Bokonon, and the instrument, the kan-kan, that brought me into my own particular karass was the book I never finished, the book to be called The Day the World Ended.
Quotation of interest:
They were lovebirds. They entertained each other endlessly with little gifts: sights worth seeing out the plane window, amusing or instructive bits from things they read, random recollections of times gone by. They were, I think, a flawless example of what Bokonon calls a duprass, which is a karass composed of only two persons.
"A true duprass," Bokonon tells us, "can't be invaded, not even by children born of such a union."
I exclude the Mintons, therefore, from my own karass, from Frank's karass, from Newt's karass, from Asa Breed's karass, from Angela's karass, from Lyman Enders Knowles's karass, from Sherman Krebbs's karass. The Mintons' karass was a tidy one, composed of only two.
[...]
Bokonon tells us, incidentally, that members of a duprass always die within a week of each other. When it came time for the Mintons to die, they did it within the same second.