1.NounA Japanese poem in three lines, the first and last consisting of five morae, and the second consisting of seven morae, usually with an emphasis on the season or a naturalistic theme.
2.NounA three-line poem in any language, with five syllables in the first and last lines and seven syllables in the second, usually with an emphasis on the season or a naturalistic theme.
"Haiku, a poem; five beats, then seven, then five; ends as it began."