Each haiku poem consists of just three lines. Other poems with strict line counts include the sonnet which always has 14 lines. In longer poems there is ample time to explore themes, and describe ideas and feelings. In the short form of haiku, each word must count.
In English, the first line of a haiku is made up of five syllables, the second line consists of seven syllables and the third line has another five syllables. "Stars fall to dark earth / splinter on a flake of glass / mirrors of cracked sky" is an example of haiku's syllabic form.
Haiku poetry does not usually rhyme at the end of the lines although there are exceptions. The main requirement is that the haiku should sound natural and not contrived. Some haiku poets prefer to rely on internal rhymes and half-rhymes instead of end rhymes.
Haiku developed out of the Japanese tanka poetry form. This consists of five lines of poetry: five syllables, followed by seven, followed by five and then two lines of seven syllables. The first three lines, called the "hokku", set the scene for the poem, typically focusing on a season or nature. At the end of the 18th century the first three lines took on an independent life as the haiku that we know today.