The print edge is the part of the canvas that gets wrapped around the wooden frame and neatly tucked in to form the sides of the print. Items I sell on canvas have a wood frame that is 1.5 inches thick, so the print edge is at least 1.5 inches wide around the image you purchased to wrap it neatly around the frame.
For small prints I offer black or white edges only so that you do not lose any of the image to fold the edges around the frames.
Larger images have a bit more flexibility to print slightly larger to use some of the image, to wrap it around the frames.
Black edge - the edges around the image are a black coating color
White edge - the edges around the image are a white coating color
Image edge - the edges around the image is either a copy of or part of the image itself.