This expression from the poem ‘Road Not Taken’ by Robert Frost means: ‘The road that he was walking on one morning got forked at one point into two roads. One of them was much traveled on, but the other was perfectly green, which implied very people had used that road.

He stood long at the point where the road diverged into two roads, not able to decide as to which of the two roads he should take. He was willing to travel on both roads simultaneously, but practically it is not possible. So he decided to take the road which appeared to have been traveled less.