The haiku is a Japanese poetic form that consists of three lines, with five syllables in the first line, seven in the second, and five in the third. The haiku developed from the hokku, the opening three lines of a longer poem known as a tanka. The haiku became a separate form of poetry in the 17th century.
These rules apply to writing haiku:
“The Old Pond” by Matsuo Bashō
An old silent pond
A frog jumps into the pond—
Splash! Silence again.
“Over the Wintry” by Natsume Sōseki
Over the wintry
Forest, winds howl in rage
With no leaves to blow.
Haiku are usually unrhymed. In Japanese, haiku are traditionally printed as a single line, while haiku in English often appear as three lines, although variations exist. There are several other forms of Japanese poetry related to haiku, such as tanka, as well as other art forms that incorporate haiku, such as haibun and haiga.
Kiru and kireji
In Japanese haiku, a kireji, or cutting word, typically appears at the end of one of the verse's three phrases. A kireji fills a role analogous to that of a caesura in classical Western poetry or to a volta in sonnets. A kireji helps mark rhythmic divisions. Depending on which kireji is chosen and its position within the verse, it may briefly cut the stream of thought, suggesting a parallel between the preceding and following phrases, or it may provide a dignified ending, concluding the verse with a heightened sense of closure.
The kireji lends the verse structural support, allowing it to stand as an independent poem. The use of kireji distinguishes haiku and hokku from second and subsequent verses of renku; which may employ semantic and syntactic disjuncture, even to the point of occasionally end-stopping a phrase with a sentence-ending particle. However, renku typically employ kireji.
In English, since kireji have no direct equivalent, poets sometimes use punctuation such as a dash or ellipsis, or an implied break to create a juxtaposition intended to prompt the reader to reflect on the relationship between the two parts.
The kireji in the Bashō examples "old pond" and "the wind of Mt Fuji" are both "ya". Neither the remaining Bashō example nor the Issa example contain a kireji. However, they do both balance a fragment in the first five on against a phrase in the remaining 12 on (it may not be apparent from the English translation of the Issa that the first five on mean "Edo's rain").
On (Japanese prosody)
In comparison with English verse typically characterized by syllabic meter, Japanese verse counts sound units known as on or morae. Traditional haiku is usually fixed verse that consists of 17 on, in three phrases of five, seven, and five on, respectively. Among modern poems, traditionalist haiku continue to use the 5-7-5 pattern while free form haiku do not. However, one of the examples below illustrates that traditional haiku masters were not always constrained by the 5-7-5 pattern either. The free form haiku was advocated for by Ogiwara Seisensui and his disciples.
Although the word on is sometimes translated as "syllable", the true meaning is more nuanced. One on in Japanese is counted for a short syllable, two for an elongated vowel or doubled consonant, and one for an "n" at the end of a syllable. Thus, the word "haibun", though counted as two syllables in English, is counted as four on in Japanese (ha-i-bu-n); and the word "on" itself, which English-speakers would view as a single syllable, comprises two on: the short vowel o and the moraic nasal n. Conversely, some sounds, such as "kyo" may look like two syllables to English speakers but are in fact a single on (as well as a single syllable) in Japanese.
In 1973, the Haiku Society of America noted that the norm for writers of haiku in English was to use 17 syllables, but they also noted a trend toward shorter haiku. According to the society, about 12 syllables in English approximates the duration of 17 Japanese on.
Kigo
A haiku traditionally contains a kigo, a word or phrase that symbolizes or implies the season of the poem and is drawn from a saijiki, an extensive but prescriptive list of such words. Season words are evocative of images that are associated with the same time of year, making it a kind of logopoeia. Kigo are not always included in non-Japanese haiku or by modern writers of Japanese free-form haiku.
From https://en.wikipedia.org/wiki/Haiku