Haiku '''haiku, is a form of Japanese poetry, consisting of 17 moras (or on), in three metrical phrases of 5, 7, and 5 moras respectively. Haiku typically contain a kigo, or seasonal reference, and a kireji or verbal caesura. In Japanese, haiku are traditionally printed in a single vertical line, while haiku in English usually appear in three lines, to parallel the three metrical phrases of Japanese haiku.