hai·ku
ˈhīˌko͞o/ noun
A haiku poem consists of three lines, with the first and last lines having 5 moras, and the middle line having 7. A mora is a sound unit, much like a syllable, but is not identical to it. Since the moras do not translate well into English, it has been adapted to where syllables are used as moras.
Haiku started out as a popular activity during the 9th to 12th centuries in Japan called “tanka.” It was a progressive poem, where one person would write the first three lines with a 5-7-5 structure, and the next person would add to it a section with a 7-7 structure.