Every poet learns through writing only. Where he is good at, and where he can improve. What is a form poetry supposed to do? And how to bring soul into a structure that needs to be incorporated. I'm no different. My understanding of the haiku to be a 5-7-5 syllable structured form, that needs absolutely strict adhering to has changed, and I am, I believe, slowly understanding the soul of the form I love to write, the one called a haiku, and it has happened over the past two years, a slow learning curve, but one going upward nonetheless.
A haiku is still less than seventeen syllables. The Japanese, when they wrote it, wrote it in the form of 5-7-5 Japanese syllables, called "on" or "morae". When the same is written in English, it isn't always in the same 5-7-5 format, sometimes it's lesser too. Some few haiku see it exceed 17 syllables, but it's a rarity, and when it does, it doesn't exceed by a lot.
A perfect e.g. of the haiku not necessarily being in 5-7-5 is this one, written by a pioneer of Haiku in English, Cor van den Heuvel in the Haiku Anthology, 1999.
A haiku is still less than seventeen syllables. The Japanese, when they wrote it, wrote it in the form of 5-7-5 Japanese syllables, called "on" or "morae". When the same is written in English, it isn't always in the same 5-7-5 format, sometimes it's lesser too. Some few haiku see it exceed 17 syllables, but it's a rarity, and when it does, it doesn't exceed by a lot.
A perfect e.g. of the haiku not necessarily being in 5-7-5 is this one, written by a pioneer of Haiku in English, Cor van den Heuvel in the Haiku Anthology, 1999.
Little spider
will you outlive
me
A haiku doesn't tell what is the idea in the mind of the auther, it shows. Whereas the haiku above would just look like a direct question told out in a moment, it shows to me, a question of survival, who'll be the last standing.. if we read it in another way, we could also feel it to be a question asked with an ego, or pride... the bigger species would outlast the smaller ones. It has layers in it which are shown to the reader. One of my friends told me, it takes more than a minute to actually and completely read a haiku, and understand what the poet wishes to say. Perhaps even this breaking down might be not completely accurate, but it's more than a question to ask the spider, right? It makes you think... what's the thought behind the poet's words.
The most common thing new haijin get wrong is syllables. A syllable is different from a word. Take the word "traditional" as an example. It is one word, but it has four syllables, since we pronounce it as "tra-di-tio-nal" (tra-di-sha-nal). The haiku has less than seventeen syllables, and not less than seventeen words. So one must get that right. If you are having trouble counting them, you can refer the word you are wanting to count syllables for, at The Free Dictionary website. When they answer your query, they show the word in split syllables, so you can know how many syllables are present.
A haiku is predominantly on nature. The haikai form, senryu, encompasses the structural limitation of the haiku with seventeen syllables, but is more reflective on life and emotions. A haiga puts the haiku or senryu on a photograph, and a haibun puts it as part of a little narrative. These four haikai forms are what would be accepted by us here at Haiku Heights.
To summarize...
A haiku is a three line poem. It shows what the author wants us to understand from it, rather than tell it directly. The limitation to a haiku is seventeen syllables. It can be at maximum, that much. If you wish to go by the traditional Japanese structure even with English haiku, you can use a 5-7-5 syllable, or 3-5-3 syllable structure. If you are doing a haibun, let it be short and not a mile long story with a 3 line haiku somewhere. Try not to combine many haiku to extend the syllable count.
(Updated, 30/6/2012)
(P.S: The explanation above is only my understanding of the haiku and its forms.)
Leo.