It's a direct address to an absent person, an inanimate object, or an abstract concept as if it were present and able to respond. This technique is often used to create a sense of emotional intensity or to emphasize a particular idea.
Here are some examples:
* "O, Romeo, Romeo! Wherefore art thou Romeo?" (Shakespeare's *Romeo and Juliet*) - Juliet addresses Romeo, even though he is not physically present.
* "Oh, Death, be not proud!" (John Donne's "Death Be Not Proud") - The poet addresses death as if it were a person.
* "Twinkle, twinkle, little star, How I wonder what you are." (Traditional nursery rhyme) - The speaker addresses a star, even though stars cannot respond.
Apostrophe can be a powerful tool for poets, allowing them to express strong emotions and create vivid imagery.