expression, godan verb (-ru)
compose a haiku poem
Specifically refers to creating a haiku, not just any phrase or sentence. The word 句 here means a haiku verse.
彼は毎日一句を作ることにしている。
He makes it a rule to compose one haiku every day.
この景色を見て、思わず句を作った。
Seeing this scenery, I spontaneously composed a haiku.