In digital photography, transparency is the functionality that supports transparent areas in an image or image layer. Certain image formats do not support transparency. Opacity is the extent to which something blocks light. You can change the opacity of layers, filters, and effects so that more (or less) of the underlying image shows through.
"TASTY" becomes transparent when its opacity is set to 50%. Note that "SANDWICHES" opacity is set to 100% so it is opaque, or not transparent.