form

This is a huge topic in poetry.  

Poets like to organise their thoughts into specific forms.  

Often in poetry of the past, these forms would be quite complex.  Much modern poetry in English tends to feature less complex forms, often allowing poets to create an impression of directness or spontaneity.

Verses or stanzas are the correct label for organised groups of lines.

Couplets are pairs of lines.

Tercets are stanzas made up of three lines.

Quatrains are stanzas made up of four lines.

You don’t need to worry about memorising the technical names for all the different stanza-forms (and there are many more), but you should comment on (and explore) the effect of the form which a poet chooses.  

For example, a poem made up of a sequence of four-line verses may result in a poem whose ideas are clearly sequenced - the form might give a logic and order to what is being said.  Or in another such poem, it might give a framework, out of which the poem’s ideas seem to break free.  

Exploring the effects of form is essential in your commentary, but make sure, as always, that you don’t just describe the feature.  You need to explore it.

Here’s an example of description:

This poem about tigers is set out in a sequence of three four-line verses.

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Here’s an example of exploration:

This poem about tigers achieves poise and power through the poet’s choice of form: the three four-line stanzas establish a sense of thoughtful order, perhaps echoing the dignity of these massive creatures, something which contrasts with the vivid language describing the power and speed of the tigers’ movement.

Free verse has often been used by poets writing in English over the past hundred years or so.  

This form can feature varied stanza or section lengths and usually features little or no rhyme.  Rhythm will be irregular too.  All these choices might establish a sense of the poem being close to the sound and features of everyday talk, establishing perhaps a sense of authenticity or spontaneity.  Be aware of the varied rhythmic effects in a free verse poem: these may replicate those of everyday speech, but in powerful and striking ways.