What is a poem about called?

The subject of a poem is often referred to as the poem's theme or topic. The theme is the central idea or concept that the poet explores in the poem. It can be an emotion, an experience, a philosophical idea, or any other subject that the poet chooses to write about. The theme of a poem is often conveyed through the use of imagery, symbolism, and other literary devices. The poet uses language and imagery to create a vivid and meaningful representation of the theme.