Sestina is a highly-structured poem containing thirty-nine lines, designed using six sestets followed by a single tercet.

True

Explanation:

The given statement is true.

The sestina is a fixed form of poetry that consists of seven stanzas - six sestets (stanzas consisting of six lines) and one final tercet (a stanza consisting of three lines). It's usually unrhymed.

Another characteristic of this form of poetry is that the last words of each line of the first stanza are repeated in a different order as the last words in each following stanza. The closing tercet contains all six words - two per line, placed in the middle and at the end of each line. You can see an example in the image shown below: