Opacity is a measure of how opaque or transparent an object (i.e. line, polyline, text, symbol, image, metafile, fill, contour fill, layer, foreground, background, etc.) is. A value of 100% opaque means there is no ability to see through the object. A value of 0% opaque means there is full ability to see through the object, or fully transparent. A value between zero and 100 percent indicates some ability to see through the object, also referred to as semi-transparent.