The sestina is a traditional poetic form popularized by the likes of Dante Aleghiri, but one that rose to popularity among contemporary poets such as Elizabeth Bishop and Robert Lowell.
Pattern: the sestina has six stanzas of six lines each, and a final stanza of three lines. (39 lines in total). The final stanza is called the envoi.
The repeated word at the end of each line is called a teleuton.
Here is a definition from the Academy of American poets: Sestina
This exploration of the sestina from Classical Poets website offers a clear description and common uses of the form. The description shows how the “spirals” in on itself