The Brick Wall
From Homestar Runner Wiki
The Brick Wall stands just a few steps from Homestar Runner's door. In The Best Decemberween Ever, Homestar and Strong Sad stand behind The Brick Wall and discuss Strong Bad's Decemberween present. It has since become somewhat of a staple of Decemberween toons, though it has made appearances in non-holiday related toons, as well.
The wall is a reference to the comic strip Peanuts, in which Charlie Brown and his friends stand behind a similar wall.