Defamiliarization is a literary trick whereby the writer takes something ordinary/everday and helps the reader to see it in a new light. Because some things are so familiar to us (things we see every day, for example, and just walk on by) we often fail to see the drama or beauty such objects contain. To figure this technique out in relation to The Road Less Traveled, let's take a look at the poem itself...obviously, the roads are the focus of the poem. A path in the woods is perhaps something people don't stop to think about. After all, a path is just a way to get from here to there. It, in itself, is not normally thought of as a pretty thing (though the landscape around it may be pretty.) So by taking something so functional and commonplace, like a path, and making the reader see it as something greater, Frost is practicing defamiliarization.
"Two roads diverged in a yellow wood,And looked down one as far as I couldThen took the other, as just as fair,And both that morning equally layI shall be telling this with a sighAnd that has made all the difference.
I have put some interesting parts in boldface. Someone walking down a path in the woods would not think of it as "fair" and something that wants "wear." And who would think that the simple choice of a path could "make all the difference" in one's life? This poem gives a certain weight and power to an object that is most often used and not thought about. Perhaps a little of the glory is lost today (a path in the woods isn't quite as commonplace now as it would have been back then, now-a-days it would probably have to be about a sidewalk) but the elevation to power of the common foot path by this poem "makes all the difference" to the reader.