What is the poem "Harlem," by Langston Hughes, about? Write about what you think each line means.

First, the speaker asks, "What happens to a dream deferred?"  By this, he seems to be asking the fate of a dream that has been put off or postponed.  The poem is sort of an exploration of all the things that such a dream might feel like, ending in what seems like an inevitable eventuality.

Then, he lists several comparisons, mostly similes in which he points to the similarity between dream deferred and something else. The line "Does it dry up / like a raisin in the sun?" compares the put-off dream to a hard little dry raisin that is no longer enjoyable or even edible.  It was once probably sweet and tasty.  Then he asks, "Or [does it] fester like a sore -- / And then run?" comparing the dream to an open wound that has putrefied and begun to ooze pus.  So, this wound is something that could have been taken care of, but instead of healing, it has become infected and painful.  Next, he asks if the deferred dream "stink[s] like rotten meat?"  Again, something that could have been nutritious and delicious has become unusable, a nuisance, something that everyone in its vicinity is aware of because the smell is so grotesque.  Finally, he asks if the dream "crust[s] and sugar[s] over -- / like a syrupy sweet?"  Here, he compares the dream to something that might once have been tasty and choice but has become kind of sickening over time.

In the final simile, he suggests that the dream "sags / like a heavy load."  This means the dream would weigh one down rather than lift one up.  The dream, put off or to the side, is not an inspiration, the way we typically think of dreams, but a burden to bear.  Finally, in the only metaphor of the poem, the speaker suggests that the dream deferred will "explode," like a bomb.  In this comparison, the dream does damage and affects everyone with a violent force.  If a person, then, is forced to ignore their dreams, or if they are constantly told that their dream cannot be achieved just now, they are eventually going to get angry, and that anger could boil over in such a way that their dream can no longer be ignored.  Because the poem is called "Harlem" and because the poet is African American, many people interpret the dream, here, as the dream of racial equality in America, although it could apply to many different dreams.