one of several parallel layers of material arranged one on top of another (such as a layer of tissue or cells in an organism or a layer of sedimentary rock)
"The geologist carefully examined each stratum of the ancient cliff to determine the age of the fossils found within them."
people having the same social, economic, or educational status
"the working class"
"an emerging professional class"
a subpopulation divided into a stratified sampling
"The researcher selected participants from each income stratum to ensure the survey results accurately reflected the entire population."
One of several parallel horizontal layers of material arranged one on top of another.
"The geologist carefully examined each stratum of rock to determine how many years had passed since the volcanic eruption."