Coaster/ˈkəʊstər/ Definition 1 of 4Pro Tip 1/3Protect Surfaces Use 'coaster' to refer to protecting tables from heat or liquid damage. I need a coaster for this hot pot. Pro Tip 2/3Decorative Items 'Coaster' can refer to decorative objects, not just functional ones. Check out these beautiful marble coasters. Pro Tip 3/3Social Etiquette Using a 'coaster' can be a sign of good manners in someone's home. Please use a coaster for your drink.