A hokku is the opening three-line verse of a linked Japanese poem such as renga. It traditionally has a 5-7-5 sound pattern and sets the tone, season, or scene for the rest of the sequence. The hokku later developed into the modern haiku, but the two are not identical: hokku was originally a starting verse, not a stand-alone poem.
Example
Winter road at dusk
one crow on the fence post waits
for the moon to rise