From Latin, The Art of Poetry. Horace's version of Noding about Noding, and also coincidentally his most famous work.

Dated to 13 B.C, Ars Poetica presents Horace's views, or if you may, directives, of the art of poetry and Poetics in general.

Ars Poetica wasn't Horace's original title, and it was added later on, probably by Quintilian (who among other things complied a list of famous writers and their works).

In fact, most experts refers to it as Horace's Epistle to the Pisos, or for us simpletons: Horace's letter to a dude named Pisos.
In spite of its bombastic title, given to it by later generations, it is believed that Horace never intended to write Ars Poetica as a guide to writing poetry, but rather as a personal letter in the form of a verse.

This claim can be easily proven by referring to Horace's previous writings of the time, but the text provides the best evidences to support it; the lack of proper structure and any organized buildup of ideas and concepts, feels more like a researcher scrabbling his notes and ideas, than a writer writing his great thesis; the informal and personal writing, to Pisos (The Pisos were one of Rome's most noble families, descended from Romulus himself according to their own objective legend, and it's not clear to whom of them the letter was addressed).

As a poem about poetry, Ars Poetica, was coined as a phrase, describing self-referential poetry - a poetry which referrers to its own origins and structure (e.g. Gamaliel's above writeup).