Stratum

stratum

1. any of the distinct layers into which sedimentary rocks are divided

2. Biology a single layer of tissue or cells

3. a layer of ocean or atmosphere either naturally or arbitrarily demarcated

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stratum [′strad·əm]

(geology)

A mass of homogeneous or gradational sedimentary material, either consolidated rock or unconsolidated soil, occurring in a distinct layer and visually separable from other layers above and below.

(science and technology)

One in a sequence of distinct layers.

(statistics)

subpopulation

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stratum

A bed of sedimentary rock or earth.

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Stratum 

in geology, the principal form of occurrence of sedimentary rocks, reflecting their sequential deposition. A stratum has more or less homogeneous composition and is confined by two roughly parallel surfaces (the upper is the ceiling and the lower is the sole). The thickness of a stratum, from fractions of a meter to several meters, is much less than the length. Each stratum (with normal, undisturbed bedding) is younger than the one beneath it. Strata may also be composed of metamorphic rocks. Magmatic rocks and ores that are stratiform are called sheet deposits.

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Stratum 

a designation for social levels or classes found in certain non-Marxist conceptions of social stratification.