Tercet (or Triplet) is a stanza comprising of three lines e.g. The Old Familiar Faces by Charles Lamb.
[n] the cardinal number that is the sum of one and one and one
Synonyms
3, deuce-ace, III, leash, ternary, ternion, terzetto, three, threesome, tierce, trey, triad, trine, trinity, trio, triplet, troika