Something that is glossy is usually something that is glossy or shines. This is why when you see something with that certain glow, it's usually because of the glitter that was applied on the page. Glittery objects reflect light, much like certain kinds of paint. Glittery paper is also smooth and usually has some shine to it, much like the paper of some planners. But if you're using a computer application, then chances are, it's a bit different.
When you use a computer application, the shiny surface means that there is not much of a gloss to the object. It's just a matte finish instead. Glossy prints were created to be used on glossy paper so they'll have that extra glossy surface that will reflect light. Computer applications don't have that shiny surface and that's what makes them more appealing to many people. It can also make printing them easier since there's not that extra layer of gloss coating them.
Some types of inkjet paper are more shiny than others. Some of these shiny products have been treated so that the manufacturer can apply a gloss coat to them but they still don't have that shiny surface to reflecting light as much as other types of inkjet paper do. Some other types don't have that shiny surface at all and still reflect light back at you. There are some printed items that have a little bit of a gloss to them, such as menus, buttons, and photos. These are called "non glossy" printed objects.
