A descriptive poem is a poem that contains a large amount of descriptive detail. They might take as their subject something visual, for instance, and describe its characteristics in depth.
Descriptive poetic styles might be incorporated into narrative or lyric types of poetry. Narrative poetry is a sequence of events as told from a specific perspective, whether on an epic scale such as John Milton's "Paradise Lost" or more of a folksy ballad.
Lyric poetry, meanwhile, tends to focus on emotions and thoughts. These might be mournful, as in the case of an elegy, or joyful and celebratory, as is often the case of sonnets.