A haiku is a 17-syllable poem–with the format of 5 syllables for 1st and 3rd lines, and 7 syllables for the 2nd line. Traditionally, it was geared towards describing nature–with the intent of immortalizing one specific moment in time. Modern haiku is much more malleable, since it has evolved, into the inclusion of various niches.
To explain further, one syllable is equivalent to one “opening of the mouth,” when we pronounce a word. An example would be: story = sto-ry = 2 syllable-count.
A senryu is similar in structure to haiku, but more concerned with human nature, and is often humorous or satiric — usually in three lines of seventeen kana.
Try to make your own haiku. It’s a good way of practicing poetry, with a simple syllable count technique.