A wall is a solid vertical structure that divides, protects, or supports. In buildings, walls separate rooms from each other and hold up the roof. Outside, walls mark boundaries between properties or keep animals in their pastures. Ancient cities built massive defensive walls to protect themselves from invaders. The Great Wall of China stretches thousands of miles across mountains and valleys.

Walls can be made from many materials. Brick walls, stone walls, wooden walls, and concrete walls each have different strengths. Some walls bear weight (these are called load-bearing walls), while others just divide space.

The word appears in many expressions. When you hit a wall while working on something difficult, you've reached a point where you feel stuck and can't make progress. If someone describes a person as having their “back against the wall,” they mean that person is in a tough situation with few options. When something goes off the wall, it means things have gotten wild and chaotic. And if you're talking to someone who won't listen or respond, you might feel like you're “talking to a wall.”

People sometimes wall off their feelings, meaning they hide emotions behind an invisible barrier. This kind of wall can feel almost as real as one made of bricks.