Layers and tiers refer to the number of layers of cake in a multi-layered cake. A layer is a single horizontal slice of cake, while a tier refers to a stack of multiple layers, typically separated by frosting or filling. For example, a two-tier cake would have two separate stacks of cake layers, while a three-layer cake would have three slices of cake stacked on top of each other. When ordering a multi-layered cake, you can specify the number of layers per tier or the overall number of layers you would like in your cake.