A heptastich is a stanza or short poem made up of seven lines. Poets may use it as a complete seven-line unit or as one section within a longer poem.
Example
Morning loosens silver from the pond,
then draws the geese in restless arcs;
a fence of reeds leans after dawn,
soft with the weight of last night's rain.
The garden wakes one leaf at a time,
and every shadow thins to blue
before the sun climbs over the hill.