A haiku is a short verse of 17 syllables,
divided into units of five, seven, and five syllables.
Haiku use simple expressions in ways that allow deeply
felt emotions and a sense of discovery to be readily 
conveyed to the reader. As a rule, a haiku must have a 
word that is identified with a particular season.

The following is an English translation of a haiku by Matsuo Basho:

The autumn wind is blowing.
But the chestnut burs
Are green.