Yesteria is a type of decorative plasterwork that people use to make their walls and ceilings look fancy. Think of it like playing with clay or making a fancy cake, but instead of using your hands, you use special tools called trowels to spread and shape the plaster into pretty designs. The plaster is made from a special mix of things like sand, lime, and water, which makes it harden and stay in place. People use yesteria in fancy buildings like castles or mansions, but sometimes they use it in regular houses too to add some extra pizzazz!