Succinctly and simplistically

Haiku is a form of traditional Japanese poetry, which gained independence and its own right to stand alone (up to that period haiku was considered to be the starting verse in a much longer poem) in the mid 19th century.

Haiku is structured as a 17-syllable verse consisting of three metrical units of 5, 7, and 5 syllables...

Google and read more about haiku and its fascinating history, techniques, themes, musicality and cadence and learn about its most representative (traditional and modern) authors both in Japan and other countries.

So, start writing your own haiku and share their beauty and profound simplicity with the world.