Embossing is to raise an image up above the surface of the paper whereas debossing pushes the image down into the surface of the paper.   Both techniques provide tactile qualities as well as visual shadow lines that subtly enhance the look and feel of an object.  Either process can have color or can be blind i.e. without color.  Both embossing and debossing are produced on letterpress equipment and require film and metal dies to be made.