Source : Webster's Revised Unabridged Dictionary (1913)

Quipu \Qui"pu\, n.; pl. {Quipus}. [Peruv. quipu a knot.]
   A contrivance employed by the ancient Peruvians, Mexicans,
   etc., as a substitute for writing and figures, consisting of
   a main cord, from which hung at certain distances smaller
   cords of various colors, each having a special meaning, as
   silver, gold, corn, soldiers. etc. Single, double, and triple
   knots were tied in the smaller cords, representing definite
   numbers. It was chiefly used for arithmetical purposes, and
   to register important facts and events. [Written also
   {quipo}.] --Tylor.

         The mysterious science of the quipus . . . supplied the
         Peruvians with the means of communicating their ideas
         to one another, and of transmitting them to future
         generations.                             --Prescott.

Source : WordNet®

quipu
     n : calculator consisting of a cord with attached cords; used by
         ancient Peruvians for calculating and keeping records