A haiku is an unrhymed three-line poem. It is based on a traditional Japanese poetic form. Though there are different ways to write haiku, the traditional pattern in English is to write the first and last lines with five syllables each, and the middle line with seven syllables. In other words, the pattern of syllables looks like this:

Line 1: 5 syllables

Line 2: 7 syllables

Line 3: 5 syllables