stratum

A horizontal layer of material, especially one of several parallel layers arranged one on top of another.

A bed or layer of sedimentary rock that is visually distinguishable from adjacent beds or layers.

Any of the regions of the atmosphere, such as the troposphere, that occur as layers.

A layer of tissue.

A level of society composed of people with similar social, cultural, or economic status.

One of a number of layers, levels, or divisions in an organized system.

In archæol. excavations, one of the layers of deposits left by successive civilizations, as in the overlying cities at Hissarlik, the ancient Troy.

A layer of material, formed either naturally or artificially.

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.

A bed or layer artificially made; a course.