The Bedford Glossary of Critical and Literary Terms - Ross Murfin 2018
Triplet: A tercet (a group of three lines of verse) in which all three lines rhyme (aaa).
EXAMPLE: Alfred, Lord Tennyson’s “The Eagle: A Fragment” (1851) is composed of two triplets:
He clasps the crag with crooked hands;
Close to the sun in lonely lands,
Ringed with the azure world, he stands.
The wrinkled sea beneath him crawls:
He watches from his mountain walls,
And like a thunderbolt he falls.