Haiku is more than a type of poem; it is a way of looking at the physical world and seeing something deeper, like the very nature of existence. A haiku poem consists of three lines, with the first and last line having 5 moras, and the middle line having 7. A mora is a sound unit, much like a syllable, but is not identical to it.
Some classic examples
O snail Climb Mount Fuji, But slowly, slowly!
Everything I touch with tenderness, alas, pricks like a bramble.