Free Verse
"Hanging Fire" is written in free verse. It doesn't have a regular rhyme scheme or meter; it's not written in a tight form such as a sestina or villanelle.
But that doesn't mean that Lorde's poem is totally formless. It is made up of three stanzas, each with 11 or 12 lines. Its lines are short; most lines aren't longer than seven words. And most importantly, the poem has an important repetition; the phrase "and momma's in the bedroom / with the door closed" ends each stanza. That's what's known as a refrain.
The poem's short, simplistic form helps define the speaker for us; the poem sounds like it's being spoken by an actual 14-year-old. (Check out "Speaker" for more on her.) And the formal repetition really hits home emotionally. We know what troubles our speaker the most, and it's that she feels isolated from her mother. Lorde uses free verse to get at what it really feels like, and sounds like, to be a teenage girl.