A Haiku, when written in English, is a 3-lined unrhymed tercet.
A Poetic TERCET is essentially a verse of three-lines all of which end in the same rhyme and often written in iambic pentameter. I print three of my own such Poetic TERCETS below . . .
THE DOUBTING THOMAS
To start each morning he would kneel and pray;
He needed that to get him through the day.
At least his god would let him have his say.
He loved to speak and then have the last word.
His friends, such as they were, called him absurd,
The rest just closed their ears and nothing heard.
God said to Man I’ll give to you a choice,
Believe in me and then with me rejoice,
Or be a Trappist monk and lose your voice.