stratum

noun

• One of several parallel horizontal layers of material arranged one on top of another.
• A layer of sedimentary rock having approximately the same composition throughout.
• Any of the regions of the atmosphere, such as the stratosphere, that occur as layers.
• A layer of tissue.
• A class of society composed of people with similar social, cultural, or economic status.
• A layer of vegetation, usually of similar height.
• The level of accuracy of a computer's clock, relative to others on the network.