An extended metaphor is a comparison that says one thing is another for several lines, for a stanza, or throughout a poem. Regular metaphor is usually just a word or two, whereas an extended metaphor can span numerous lines. Simile is a comparison using words such as like or as (strong as a lion). A symbol is just one word that refers to something else (cage - boundaries, helplessness). Theme is the general topic or subject of a literary work.
