A poem was a type of literature created using the art form known as poetry. The author of a poem was a poet.
There were several well-known poems from Earth, including Iliad, The Charge of the Light Brigade, No Second Troy and The Rime of the Ancient Mariner. (DS9 novel: The Laertian Gamble; DS9 episode & novelization: Sacrifice of Angels; DS9 - Rebels novel: The Courageous)