Term: Prose Poem
A prose poem is a poem that does not use line breaks. This still allows the poet to use alliteration, metaphor, ambiguity, personification, and many other poetic techniques, but it can still be strange to see a poem that goes all the way to the right-hand margin. One thing that may differentiate a prose poem from a very short story is that the latter will have a stronger preference for narrative than the former, but this is very much debatable.
John Ashbery's 'For John Clare' is a good example, one that explores the contrast between openness and containment; as John Clare was a poet who was devoted to nature, but locked in an asylum, it could be suggested that it is very appropriate to see the subject explored without the containment that line-endings would give.