A full image wrap is where the entire image is printed and mounted around the whole frame. So there will be a portion of your image that will be shown on the sides of the canvas. The lines above show an example of where the edges of your image will be lost around all 4 sides. We only recommend this option if the focal point of the image is in the center and you don't mind the edges getting wrapped around the side of the canvas.
The mirror wrap option is by far the most popular choice because you don't lose any of your image. This is what we recommend most of the time. The whole image is printed on the front, and a portion of each edge of the image is used to extend the canvas to wrap it around the frame. The image above might look weird in 2D but the lines show the area where all 4 sides have been mirrored to wrap the canvas so that none of the image is lost.