noun one of several parallel layers of material arranged one on top of another (such as a layer of tissue or cells in an organism or a layer of sedimentary rock).
noun people having the same social, economic, or educational status.
— synonyms: class, social_class, socio-economic_class
noun an abstract place usually conceived as having depth.
— synonyms: level, layer
noun a subpopulation divided into a stratified sampling.