Since the Harlem Renaissance, Harlem, a burrow of New York City, has been tied to both the realities of oppression of black people and the expressions of black people. The title, "Harlem", perfectly captures the crossroads of this expression and oppression that Langston Hughes is referencing in his poem. Within the streets of Harlem, particularly during the Harlem Renaissance, the dreams of black creativity has been realized through spoken word, art, and music, while the blood of black people has spilled out into the same streets through racism and oppression. Harlem represents both a dream and a nightmare, art and oppression, the sounds of music filling the streets, and the sounds of guns shot by police and bodies hitting the pavement. In a few short lines, Hughes captures the essence of this reality.

In Langston Hughes's "Harlem," the author is discussing the injustices done to African Americans in America, many of whom lived in Harlem, New York; the poem is part of a larger collection called Montage of a Dream Deferred.

According to the eNotes Study Guide, "Harlem" appears in a larger collection of poems that looks at what happens when millions of people are told to wait for their dreams or denied their dreams entirely. Specifically, the dream Hughes is discussing is that of equal rights and fair treatment for African Americans in America.

He named the poem "Harlem" after a neighborhood in Manhattan, New York that had a large population of African American people. It's famously known for being host to the Harlem Renaissance. This was a time of art, literature, and hope for the African American community in Harlem. The dreams they expressed 20 years before Hughes published "Harlem" still weren't complete. They still didn't have the same rights as white Americans; they still didn't get fair treatment or equal opportunities. Hughes asks what happens when these important dreams are asked to wait. He ponders whether they just dry up, create wounds, or whether they explode out with anger.

The significance of the title is that it harks back to the so-called Harlem Renaissance, a period of great cultural and intellectual activity among African-Americans, centred on Harlem in New York City in the early twentieth century. This poem was first published in 1951, and the Harlem Renaissance is generally agreed to have ended about twenty-odd years before this date, but the issues so often discussed during the earlier period still had great relevance at the beginning of the 1950s. The prominent writers and artists of the Harlem Renaissance, of whom Hughes himself was one, had eloquently addressed the problems faced by African-Americans: the ongoing injustice and racism enshrined in the country's laws, poverty and lack of opportunities. Unhappily, these problems still existed in 1951. It was not until later in the 1950s, when the Civil Rights Movement really gained momentum, and all through the following decade, that these outstanding issues really began to be addressed. 

The poem, about ' a dream deferred,' makes the sober point that the African-American dream of racial equality and justice, expressed so memorably by the leading lights of the Harlem Renaissance, still had to materialize. In concisely effective terms, the poem poses a series of rhetorical questions about what happens to a dream or hope that continues to be thwarted. The speaking voice - which can be readily equated with that of  the poet  - queries if such a dream simply dries up (like 'a raisin in the sun'), or turns rotten, or whether there might be a more violent outcome: 'Or does it explode?' This line is the final one of the poem, and is italicized to increase the dramatic effect. Hughes is clearly implying that if the African-American search for rights and equality continues to be denied, then things might turn ugly, and the dream might then erupt into violent confrontation.  Of course, this did happen on a number of occasions before the dream of equality for African-Americans was finally advanced in the later twentieth century with the repeal of the country's most oppressive racist laws.