What is the figurative language in "The Road Not Taken"?

Robert Frost uses "the road" as a metaphor for a course not taken in life. In the first line, the narrator recalls his fateful choice: "Two roads diverged in a yellow wood." "Two roads" are a metaphor for two options. The "yellow wood" signifies an autumn light. Frost's decision to set the moment in the Fall could be a metaphor for a narrator that is in his or her "autumn years."

Like many of those faced with two good options but forced to choose one, the narrator expresses sorrow that he could not choose both—we can only walk down one path. 

In the second stanza, he muses that he initially believed that his choice was the better of the two but later thought differently:

Then took the other, as just as fair,

And having perhaps the better claim,

Because it was grassy and wanted wear;

Though as for that, the passing there

Had worn them really about the same...

The option we choose is always less appealing after it is chosen, for we wonder about the choice that we did not make. Thus, in the end, the narrator realizes that both choices were about equally good.

In the third stanza, the narrator mentions time of day: it is "morning." Morning could signify a new beginning. When we are presented with a new choice, or opportunity, this offers us a chance to do something new—even to start again. It is here, too, that the narrator recognizes the finality of his or her choice:

Oh, I kept the first for another day!

Yet knowing how way leads on to way,

I doubted if I should ever come back.

The speaker knows that once a choice is made, it cannot be undone. One must continue on the "path" that was chosen.

The final stanza reveals a kind of wistfulness for choices not made:

I shall be telling this with a sigh

Somewhere ages and ages hence:

Two roads diverged in a wood, and I --

I took the one less traveled by,

And that has made all the difference.

The "difference" is not an ode to non-conformity, as so many have thought but instead an acceptance that choices determine the outcome of one's life. The path the speaker chose is "the one less traveled by," not because it was less ordinary, but only because it looked more appealing at first. Yet, both options, or paths, were "really about the same."