What is a wall?

I believe that a wall is a barrier, a structure to keep specific thing either out of in. There are physical wall like the Berlin wall to seperate non-comunist Berlin from comunist Berlin. There is also the Great wall of China that was built to keep the Mongolians out of China. Then there are prison walls, built to keep people from breaking in, and to keep people from breaking out as well. There is even the typical house wall is built for the privacy of your own home and to keep people out of your house. Then there are mental walls. Walls put up by an indivuidual or a group of individuals to keep a certain person, or people out. A single person could put up a wall to let nobody in and not be sociable with other people, and cage themselves in. A group of people could put up a wall around a certain person or a group of people to keep them from entering into another group. All the mental walls can be very unhealthy to the people involved. Finally there are cyber walls. Walls on social networks that can be used to post things about that person. It can be used to recal a certain event, show what is happening in life, or completely embarass another person. People have been fired, beaten up, or straight up embarassed a person just by posting a single thing on their wall. It's not worth putting something bad on the wall when you're only going to hurt yourself.