metrical foot
foot *****
metrical unit

Types of metrical feet are used more or less freely, although there is often basic repetition in a line.

Octameter in poetry is a line of eight metrical feet.

In poetry, a tetrameter is a line of four metrical feet.

The metrical feet used in the poem are a mixture of anapests and iambs.

The poem is written in tetrameters (lines of four metrical feet).

However, Keats incorporates spondees in 37 of the 250 metrical feet.

A pyrrhic is a metrical foot used in formal poetry.

This means each line is made up of six metrical feet.

In poetry, a break between words within a metrical foot; a pause near the middle of the line.

An antibacchius is a (rare) metrical foot used in formal poetry.