stratum

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)

people having the same social, economic, or educational status; "the working class"; "an emerging professional class"

an abstract place usually conceived as having depth; "a good actor communicates on several levels"; "a simile has at least two layers of meaning"; "the mind functions on many strata simultaneously"