DuckCorp Dico

Found one definition

1.                 From WordNet (r) 3.0 (2006):
                   
   
   
                   
                     
   stratum
       n 1: 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)
       2: people having the same social, economic, or educational
          status; "the working class"; "an emerging professional class"
          [syn: class, stratum, social class, socio-economic
    class]
       3: 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" [syn: level, layer, stratum]