Anything made only for the purpose of looking at.  You can use any medium, as there are manY sub-area.  Ceramics, painting, drawing, multi-medium, paper.  

I usually sign up for a couple extra exhibits in the Visual Arts project area as there are many projects that can fall here. Also I enter couple extra Home Environment for extra pairings or art.  As long as it could be hung on a wall, as in add a wire or saw hook on the back.