A 'gallery wrapped' canvas is where the edge of the image is wrapped around the side of the canvas. This allows the canvas to be presentable without a frame. 

For example, a 12x16” canvas will actually have the image printed onto a 16x20” canvas so that 2” on all sides of the image can be wrapped around the frame. 1 ½” will be on the side of the frame and ½” will be on the back.