stratum in WordNet English dictionary

1. people having the same social, economic, or educational status
   "the working class"; "an emerging professional class"
   class  stratum  social class  socio-economic class 
   
2. 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"
   level  layer  stratum 
   
3. 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)
   stratum