“Ars Poetica” is a term that means the art of poetry or the nature of poetry. The art of poetry refers to what makes poetry different from other types of writing. The nature of poetry refers to the ways poetry is different from prose in its expression of meaning. Since Ars Poetica is about how poetry works, an Ars Poetica poem is a poem about poetry. This would be like writing a song about a song or writing a book about writing.
Archibald MacLeish’s poem, aptly titled “Ars Poetica,” is an example of an Ars Poetica poem because it is his poetic description of what a poem should be. He notes that a poem should transcend its words (“be wordless”). The poem ends with the often quoted:
A poem should not mean
In transcending words, and being silent and free as a flight of birds, MacLeish’s view is that a poem is equal to a natural, meaningful event or image; not just a representation of words and phrase.