that seems to be what wikipedia says
"Few modern English haiku poets use the 5-7-5 syllables rule, which is often inappropriately taught in schools. The 5-7-5 practice produces a haiku much longer than a traditionally composed haiku in Japanese, as the Japanese do not count syllables as they are defined in English, but instead count morae (singular mora), units of time. Morae are generally shorter than the average of English syllables which are highly variable in length"
en.wikipedia.org/wiki/Haiku
(1, Wed 8 Sep 2004, 17:56, archived)