According to Wikipedia, "erasure poetry, or blackout poetry, is a form
of found poetry or found object art created by erasing words from an
existing text in prose or verse and framing the result on the page as a
poem. The results can be allowed to stand in situ or they can be
arranged into lines and/or stanzas."
"Writers and visual artists have adopted this form both to achieve a
range of cognitive or symbolic effects and to focus on the social or
political meanings of erasure. Erasure is a way to give an existing
piece of writing a new set of meanings, questions, or suggestions. It
lessens the trace of authorship but also draws attention to the original
text."