The speaker of this poem recalls a particular evening during one "bleak December." December is a rather gray month, cold and dreary, and so the speaker refers to it as bleak; further, he is absorbed by thoughts of his newly-dead lover, Lenore, and so these ruminations likely add to the mood of gloom and sadness. The speaker also claims that he remembers this evening "distinctly," meaning that he remembers it very clearly and in great detail. (This is likely for a couple of reasons: he was grieving, and some strange things happened, things about which he is going to tell us—and these happenings would cause him to recall the night with some clarify.)

Next, the speaker uses a metaphor—a comparison of two unalike things in which one is said to be the other—to describe the fire in the grate, which is going out. An ember is a glowing fragment of a fire, perhaps a smoldering piece of wood or coal. The narrator has been dozing at his desk for some time, reading an old book, and so he has probably not added any fuel to this fire recently. As the fire "died," the embers would go out as well, and so he compares them to "ghosts." These word choices, like bleak, also draw attention to the speaker's mood and help to set the mood of the text.