stratums

noun pl. strata stra′ta (-ə) or stratums -·tums

1. a horizontal layer or section of material, esp. any of several lying one upon another; specif.,
   1. Biol. a layer of tissue
   2. Geol. a single layer of sedimentary rock
2. a section, level, or division, as of the atmosphere or ocean, regarded as like a stratum
3. any of the socioeconomic groups of a society as determined by birth, income, education, etc.

Etymology: ModL < L, a covering, blanket < stratus, pp. of sternere, to spread, stretch out, cover: for IE base see strew