Edgar Allan Poe's poem The Raven is considered a classic of gothic literature. A man, probably of middle age, sits alone in his well-adorned library one cold, "bleak December" evening, and contemplates the dissolution of his relationship with "the lost Lenore." He is clearly heartbroken, but becomes uneasy when a mysterious tapping on his chamber door captures his attention. Attempting to ignore it, the unidentified source of the unwelcome noise continues to distract him. As he focuses on the possible nature of this disturbance, his mind goes back to the source of his sorrow, "the rare and radiant maiden whom the angels name Lenore." Poe's poem continues with its haunting theme, the narrator unable to grasp the meaning of this persistent intruder:
"Deep into that darkness peering, long I stood there wondering, fearing, Doubting, dreaming dreams no mortals ever dared to dream before; But the silence was unbroken, and the stillness gave no token, And the only word there spoken was the whispered word, “Lenore!” This I whispered, and an echo murmured back the word, “Lenore!”— Merely this and nothing more."
The intruder, of course, is a large black raven, which moves about the library, responding to the narrator's queries regarding its purpose with the phrase "Nevermore." The raven's continued presence and repetitive use of that phrase proves increasingly maddening to the narrator, who only wants the large bird to leave. As the bird perches atop a bust of the mythological figure of Pallas, the reader is left to conclude that this bizarre interloper signifies the narrator's emotional demise.
One of the most famous poems in history is “The Raven”, mostly because of the refrain, “Nevermore.” The speaker is a man who is grieving for the lose of his beloved Lenore, and has been visited by a talking bird who repeatedly quotes the single word, “Nevermore.” The narrator is so filled with grief over his loss that his imagination allows the bird to become transformed into a prophet bringing news that they will “Nevermore” be together, not even in heaven. As mentioned in the previous answer, the link below offers a superior summary of the poem.
Enotes provides a thorough summary of "The Raven" at the link below. Basically, the poem is about a man whose sitting alone in his house. His love has died and he is mourning her loss. A raven shows up at the door and the man begins to dialogue with the raven about his lost love, Lenore. He starts asking the raven questions, wondering if he will ever get over Lenore or if he will see her again. The raven's only response is "Nevermore".