An unrhymed Japanese poem recording the essence of a moment. Nature is combined with human nature. It usually consists of three lines of 5/7/5 (5 kana in the first line, 7 kana in the second line, and 5 kana in the third line) totaling seventeen kana.
A foreign adaptation of 1, usually written in three lines totaling 17 syllables or LESS.
Haiku is not written in the past, nor does it cover a long period of time.
Haiku usually contains a season word (called kigo). It is not a requirement, but season words are a big part of haiku.
Personal note: while I ain’t a pro at Haiku, I find some Haiku’s written devoid of anything to do with seasons or nature. While it may be completely a poet’s liberty and rightly so I personally find Haiku’s with a comparison of nature and human nature beautiful.