A layer of material, often one of several parallel layers, arranged one on top of another. The geologist examined the stratum of rock to determine its age.
A level or class to which people are assigned according to their social status, education, or income. The study focused on the economic stratum of the population most affected by the policy changes.
A layer of tissue in an organism, especially one of a number of layers in an animal or plant. The skin is composed of several strata, each with a specific function.