It means unclear or unknown
Autobiography. This includes the important points/details about a person - crucial people and events they have encountered as well.
It's always important to understand the difference between tone and mood.
I like to say that tone is how the author feels about the work. You can tell how the author feels by the word choices (diction) he or she makes.
Mood is a more personal reaction. How does the work make you feel?
If I am looking for what the tone of this poem is, I'd look at words like "diverged" and "sorry" in the first stanza and the phrase "wanted wear" in the second stanza and the lines "I doubted if I should ever come back" and "I shall be telling this with a sigh" in stanzas three and four. I might make the conclusion that the tone of this poem is one of longing.
As far as the mood goes, you might end up using the same lines and word choices as in the paragraph above. But the mood is going to be a different answer. How do you feel as a reader? Sad? Somber? Hopeful? Anxious?
As a reader, you are never sure the poem's speaker made the right choice. So that's why the mood is left up to you.
