Hey, do you know that Haiku includes seasonal reference? Things like spring, summer, autumn, winter? I certainly didn't know that! What does frog jumping into an old pond has anything to do with season? It turns out that "frog" indicates spring, which connotates newness, while being juxtaposed with old pond, which connotates oldness. That's very clever!
Reading this article by Robert Lee Brewer, Writer Digest Feb 2008 p. 83, it turns out that Haiku comes from Hokku, which is a starting verse of Renga. Then the seasonal reference makes sense. "Once upon a time in a faraway place..." and all that.
What if your Haiku does not include seasonal reference? Then it is Senryu.
Furthermore, what is the structure? Obviously, Japanese Haiku has 5-7-5 syllables, but how about English version? You can stay with the form, but translating Japanese Haikus to English ones means less syllables. So, I guess free-form Haiku is OK.
I shall be content,
brimmed, satisfied, and happy
when Hell freezes over.
Five stages of dying:
Anger, Denial, Bargaining,
Compromise, and Acceptance.