Traditional form- unrhymed 17 syllable poem of Japanese origin. It usually has a seasonal reference. The structure is: line 1 - 5 syllables; line 2 - 7 syllables; line 3 - 5 syllables
It is a lovely verse form and can say a lot in 17 syllables. See the example below.
I have not written one in a long time and will not attempt it today as I am suffering from a brain fog this morning. But do give it a try as we celebrate Haiku Day today.