Something that is glossy is something that shines or is attractive. Things that are glossy reflect light, like certain types of lipstick. Glossy paper is smooth and has a shine to it, like the paper of most calendars.
The word glossy sounds a little bit like the word glassy, which is a good way to remember it. Things that are glossy sort of look like glass, meaning they have a shine to them. After your teeth are cleaned, they'll hopefully look glossy. When you print photographs, you can choose a glossy finish — that’s when the image looks shiny and smooth. In that instance, the opposite of glossy is matte, a sort of rougher finish that doesn’t reflect light.