So called "experiments in patterns in sound." Theoretically, they are supposed to be roughly equivalent to the colors, shapes, and designs that are not in reality, it's the words that are the important parts of the poem. Ex. from Dame Edith Sitwell:

Nobody comes to give him the [rum} but the
Rim of the sky hippopotamus-glum

The sound of the words are more important than the meaning of the words.

The forms of poetry.