There is an interesting part of August Wilson's description of the setting in which his play Fences takes place:
"The yard is a small dirt yard, partially fenced, except for the last scene, with a wooden sawhorse, a pile of lumber, and other fence-building equipment set off to the side."
Fences are, obviously, barriers—obstacles to be respected or to be overcome. They not only present physical barriers, but psychological ones as well. They tell those within that they are either safe from the outside, or that they are constricted in their movement. They tell those on the outside that they are barred from entry unless explicitly invited inside. In Wilson's play, fences represent all possible meanings. They represent the barriers that kept this once-promising athlete, Troy Maxson, from having a lucrative career in professional sports (specifically in baseball), but they also represent the barriers he has created that keep those to whom he is closest from achieving their goals. Consequently, it is not only Troy who feels the duality of barriers; it is those around him who also define their existences in such terms. Note the following opening to Scene II, in which Troy's pragmatic but compassionate wife, Rose, sings about "fences":
SCENE II: The lights come up on Rose hanging up clothes. She hums and sings softly to herself. It is the following morning.
Rose (sings): Jesus, be a fence all around me every day Jesus, I want you to protect me as I travel on my way. Jesus, be a fence all around me every day.
Rose views fences in the positive sense as protection against a forbidding world; she also, however, recognizes the barriers her husband has placed in the path of their son, Cory, who aspires to a career in professional football but whose path is, it turns out, blocked by his father. Troy spends his days lamenting what could have been while simultaneously constituting a willing obstacle to his own son's ambitions for a better life. "Fences" are a motif that run throughout Wilson's play. The title is highly symbolic.
Fences are significant of many things in this play. In fact, fences means different things for different people. For example, Rose believes the incomplete fence surrounding the home will maintain her family safe inside it. However, Troy believes the fence keeps people out . After the death of Alberta, Troy finishes building the fence as a way of keeping Death, a character in the play, from claiming anyone else.
Fences meant something else for Troy as well. He constructs a fence surrounding his son Cory in order to keep him from his football dreams, thus creating an invisible "fence" in their relationship.
This answer is both superficial and irrelevant to the overall meaning of the play, sure you can summarize what the fence literally does, but figuratively, it symbolizes Troy's "fencing" in of people's lives. He fences Lyons in because he is never there for Lyons, so Lyons grows up without a father or role model. He fences in Cory by treating him unfairly and not signing his football contract, limiting Cory's opportunities for success. He fences in Gabe by signing him away to the asylum for his pension. And he fences Rose in with the responsibility of a child that is not hers. This is the figurative meaning of the title fences.