A Triolet is a type of poem that is made up of eight lines, also called stanzas, and has a specific rhyming pattern. Historically, the triolet was first seen in European literature - specifically French literature - reportedly dating back to the 13th century. It was not until much later in time, around the 1600s, that the triolet was discovered or first seen in literature written by American authors.
The triolet is a unique poem requires that both the first and second line to be repeated. With that said, there are actually less than eight lines that the writer has to generate original content for. Note that the first line is repeated three times - at the fourth and seventh lines - while the second line is repeated once, at the eighth line. The repetition of the aforementioned three lines is where triolet - "triplet" or often referred to as "the round poem" - derives its actual name. Thomas Hardy, English author and poet who passed away in the 1920s, is one of the most famous figures to have explored the triolet with his poem entitled "How Great My Grief".