Haiku has Japanese origins and is a specific type of poem.
A Haiku consists of 3 lines and 17 syllables. Line 1 has 5 syllables, Line 2 has 7 syllables, and Line 3 has 5 syllables again. Please note that instead of syllables, in its Japanese form, a Haiku poem consists of 5, 7 and 5 moras. A mora is a sound unit, much like a syllable, but is not identical to it. Since the moras do not translate well into English, it has been adapted to where syllables are used as moras. In a Haiku poem, although the theme is usually nature, but it is not always the case.
The below video will help you write your own Haiku poem.
Here are a few Haiku examples from literature: