The "waka" is the oldest form of Japanese poetry, used centuries even before the more commonly known haiku. "Waka" actually means "Japanese poem" and consists of five lines of thirty-one syllables. The first and third line contain five syllables, while the other three contain seven. The waka is often divided into an "upper verse," the first three lines, and a "lower verse," the final two lines. Traditionally lovers as well as persons of important social standing used waka poems to communicate. Waka poems are noted for their attempt to capture feelings, rather than explain them. A waka is also sometimes called a "tanka;" they share identical structures.
A "Renga" is a variant of the waka. A renga alternates between between the upper and lower verses of a waka poem up to one hundred verses. A renga follows the syllabic pattern 5/7/5/7/7/5/7/5/7/7. Interestingly, different poets often supply verses in a single renga poem, on the same theme. Like the waka, the renga focuses on images and does not normally follow a narrative.
The "haiku" is similar to the "upper verse" of a waka poem. While the form of the haiku has changed somewhat over the centuries, today the haiku consists of 17 syllables, five in the first line, seven in the second and five in the third. None of the lines rhyme; rather, a haiku attempts to freeze a particular image in a few concise, highly descriptive statements.
Like the haiku, a senryu poem contains one line of five syllables, one of seven and one of five, for a total of 17 syllables. The senryu form began with the poet Karai Senryu (1718-1790) and satirizes its subject. Senryus often expose human failings for a humorous effect, unlike the haiku, which aims for a more sublime tone in its description of nature.