The 5-7-7 waka form described as the shortest type of waka is Katauta.
Katauta consists of three phrases containing 5, 7, and 7 on, the rhythmic units used to measure classical Japanese verse. Its name means “half-poem,” reflecting its traditional role as one half of a paired exchange, often completed by a second katauta.
This format is shorter than the better-known tanka, which follows 5-7-5-7-7. It also differs from sedōka, which essentially joins two 5-7-7 sequences, producing the pattern 5-7-7-5-7-7. These related forms show how early waka could be structured for dialogue, response, or repetition.
Katauta appears in ancient Japanese poetic records, including the Man’yōshū, but it did not remain a major living form. By the Heian period, most forms other than tanka—and to a lesser extent chōka—had largely fallen out of use. Modern readers therefore most often encounter katauta in discussions of early waka history rather than in contemporary poetry.