the.com/stratum

means One distinct layer within a stack of layers — whether of rock, society, or anything else arranged in levels — defined by its position relative to the others.

from Straight from Latin stratum, meaning 'something spread out' or 'a covering,' the past participle of sternere, 'to spread, stretch out, or lay flat' (the same root that gives us 'street,' originally a road laid down or paved). Geologists in the 17th-18th century borrowed it for rock layers laid down flat over time, one spread atop another — and from there it spread, so to speak, into talk of social strata, each one laid down and pressing on the ones beneath it.