Traditional Japanese haiku carry an unrhymed, three line, 5-7-5 syllabic (beat) structure with a seasonal reference. Over the years, English Language haiku authors have transplanted the traditional Japanese structure into their own language with varying degrees of success. The 5-7-5 structure continues to define haiku for many people, and, despite it falling out of use in modern times, it is still taught to students everywhere.

Modern haiku artists take a more organic approach to haiku, one that is perhaps closer in spirit to the Japanese tradition. Contemporary English Language haiku artists have largely abandoned the 5-7-5 structure, viewing it as archaic, and tend to gravitate toward shorter syllabic counts more representative of their Japanese counterparts. Additionally, in light of many people living in urban centers, the requirement for a seasonal or nature reference has been loosened. At DailyHaiku we strive to represent a wide range of contemporary haiku and have a bunch of zen-like fun doing it.

For further information about the structure of modern and traditional haiku (and related forms), a concise and extremely useful set of definitions has been put forward by the Haiku Society of America.

(Source: http://www.dailyhaiku.org/info)