sestet
noun
ses·tet ses-ˈtet 
: a stanza or a poem of six lines
specifically : the last six lines of an Italian sonnet
Example Sentences
Recent Examples on the Web This 14-line pseudo-sonnet roughly follows the structure of a Petrarchan sonnet with its octave (first eight lines) stating a tension and the sestet (final six lines) including a volta (or turn). 
New York Times, 5 May 2022
New York Times, 5 May 2022 Word History
Etymology
Italian sestetto, from sesto sixth, from Latin sextus — more at sext
First Known Use
circa 1859, in the meaning defined above