Definitions for "Transparent image"
An image with an opaque background that looks like it "floats" on the background of a Web page. To create an image with a transparent background, you need a tool to convert the image to GIF 89a format. Then you can select one color of the GIF image (e.g., the background if it is one color) and define it as transparent.
Images that contain transparency information. Currently, this is restrictive to GIF images where only one color can serve as the transparency color.
an image that allows part of the background surface to be visible