An isometric poem or stanza is composed of lines of uniform length. In traditional poetry, most poems were isometric, adhering to a set line length throughout. For example, this stanza by William Blake is isometric:
Phoebe dressed like beauty’s queen,
Jellicoe in faint pea-green—
Sitting all beneath a grot,
Where the little lambkins trot.
All the lines are seven syllables, or four feet, in length. In this stanza, the lines are metrically identical, but isometric poems and stanzas may also have metrical variations.
The opposite of isometric is heterometric, meaning composed of lines of varying length.