Tone

Definition: the attitude the poem implies
Example: "People never believe you." 
                       -Holden Caulfield
Significance: Without a tone, a poem would be boring, flat statements. It gives the poem a sort of personality.

Interpretation

Definition: one's own view of another's figurative work
Example: In the poem "if" by Rudyard Kipling, the line "keep your head" can be interpreted as keeping your sanity.

Significance: The reader of a poem always interprets what they read.

Metaphor and Extended Metaphor

Definition: comparing two things without using like or as; an extended metaphor is a group of metaphors that originate from the same metaphor.
Example: 

"All the world's a stage, And all the men and women merely players They have their exits and their entrances"                  -William Shakespeare
Significance: Both of them make a poem more interesting.

Speaker

Definition: the one that is in and telling the poem
Example:" Upon a fuzzy vista – vision blurred –
I tried to focus; nothing ever solid
Came to view, but undeterred, I blinked
An eye to try again. Through the mist
A coloured hue; polychromatic flames
Had flickered at a whim; a rhythm bore
A thrumming too: a naturalistic hymn.
Behold! Were I to find a synonym to
Reproduce or recreate
The apparition of a butterfly,
Evolving through the waning vapour,
Drawing on a sigh from this romantic.
Glory be! The raging sun above
Had fired his furnace, flaming off
The hangers on. Now I saw the flare:
His time has come. He spread a tortoiseshell –
A scene of Mother Nature at her best.
I lay in peace in knowing I was blessed."
                                       -Mark R Slaughter

Significance: A piece of writing has to have characters to make it interesting. So poets have speakers.

Symbol

Definition: an image that is metaphorical rather than literal

Example: "Rose, thou art sick!

               The invisible worm

               That flies in the night,

               In the howling storm,

               Has found out thy bed

               Of crimson joy:

               And his dark secret love

               Does thy life destroy"

                      -William Blake

Significance: Symbols reinforce meaning in the poem. They make the poem better by helping the reader understand what is happening in the poem.

Couplet

Definition: a stanza with two lines
Example:
"A little learning is a dangerous thing;
Drink deep, or taste not the Pierian spring."
                                      -Alexander Pope
Significance: A couplet adds rhythm, and sometimes rhyme, to the poem to give a lasting impression. 

Stanza

Definition: a paragraph in a poem

Example:
"Do not go gentle into that good night,
 Old age should burn and rave at close of day;
 Rage, rage against the dying of the light"

                            -Dylan Thomas

Significance: It adds rhythm to the poem. A stanza divides the poem so it isn't a blob on the paper so the reader doesn't get confused.