Answer:
A burden.
Explanation:
Langston Hughes's poem "Harlem" is a short poem of just 11 lines that talks about a dream that is deferred and remains unfulfilled. The poem is a thought-provoking piece that talks of how unfulfilled dreams deferred for long would end up leaving a person helpless and even hopeless.
In the poem, the speaker talks of a dream deferred as a "heavy load" that "sags". In this particular phrase, the speaker meant to say that like a heavy load that sags and makes a person struggle with the heavy burden, a dream deferred can also be a massive burden for the person, leaving him desperate and uncertain of what is there in the future.
Thus, the phrase "a heavy burden" means a burden that a person has to carry.
