Haiku is an ancient Japanese form of poetry. But you already know that if you have read some before.
My haiku takes the ancient 5-7-5 form but tends to vary a bit in other ways. Often I like the last line to do more than just provide a contrast to the rest. I like it to continue the story, or perhaps, make the point more strongly, or to be related in some way to the story but, perhaps, supply a surprise ending. Haiku should be self-contained and need no outside explanation or reference to make its point.
Some are simply stories, some have deeper meanings if you sit and think about them. Some are new, some are old. Some are just plain weird.