Stratum \Stra"tum\, n.; pl. E. Stratums, L. Strata. The latter is more common. [L., from sternere, stratum, to spread; akin to Gr. ? to spread, strew. See Strew, and cf. Consternation, Estrade, Prostrate, Stratus, Street.]

1. (Geol.) A bed of earth or rock of one kind, formed by natural causes, and consisting usually of a series of layers, which form a rock as it lies between beds of other kinds. Also used figuratively.

2. A bed or layer artificially made; a course.

Source: Webster's Revised Unabridged Dictionary (1913)