A group of 3 items, especially 3 identical items; the word triplet is also used for one member of such a group. Mathematicians prefer triple for an ordered string of three elements
Russ Rowlett (Director), How Many? A Dictionary of Units of Measurement, Center for Mathematics and Science Education University of North Carolina, USA 2005. http://www.unc.edu/~rowlett/units/dictA.html, (Unit of Meas and Covr Factors - Amer) {608}