something that stands for or suggests something else by reason of relationship, association, convention, or accidental resemblance; especially : a visible sign of something invisible".

The example given is "the lion is a symbol of courage" The woods and sleep are symbols.

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"met·a·phor

a figure of speech in which a word or phrase literally denoting one kind of object or idea is used in place of another to suggest a likeness or analogy between them"

The poem is a metaphor for the poet's thoughts on his life.