Final answer:
In a poem, when an imaginary character speaks to a silent listener, it is called a dramatic monologue.
Step-by-step explanation:
When an imaginary character speaks to a silent listener in a poem, it is called a dramatic monologue. In a dramatic monologue, the speaker reveals their thoughts and feelings to an unseen listener. The speaker could be a fictional character or a persona created by the poet, and the silent listener allows the speaker to express themselves freely. Robert Browning's dramatic monologues, such as "My Last Duchess," are famous examples of this poetic form.