A poem's mood refers to the emotions evoked by the poem's language. When poets use words to specifically inspire feelings of sadness, anger, joy or other emotions, those words contribute to the poem's mood.
Nearly every poem has a mood. Robert Frost's "The Road Not Taken" uses words like "fair" and "grassy" along with the opening description of a "yellow wood" to create a specific mood: In this case, that the narrator is traveling through a beautiful, peaceful wood. Although the narrator's choice between the wood's two paths is difficult, the wood itself is calming and tranquil, and the poem's mood is the same.
It is important to know how to distinguish mood from tone. In poetry, mood refers to the emotions generated by the subject of the poem. Tone, on the other hand, refers to the point of view the author takes towards the subject. This point of view can also be described in terms of emotion, which is why tone and mood are often confused.
Edwin Arlington Robinson's famous poem "Miniver Cheevy" is an excellent example of how to distinguish between mood and tone. The language generated by the subject of the poem evokes a mood of restlessness and despair. However, Robinson's tone pokes fun at poor despairing Miniver Cheevy. Tone and mood do not always involve the same emotions.