Tone is the feeling that the author expresses in his or her writing. Keep in mind that this is different from mood, which is the feeling that the reader feels when reading the passage.
Mood and tone are not always the same. For example, the author can have a tone of pride, which can give the readers a mood of disgust, depending on the context. In another example, if the author has a tone of anger, the mood can be fear, sadness, or anger, once again depending on the context of the poem.