Think of a cut cliff again, but now you are describing it: this rock is stratified. It has bands, the bands are in order, and you can see the lines between them. Every use of the adjective can be thought of as pointing at something and saying it is built in stacked bands — rock, a society, or a set of data someone has cut into levels.
From the picture
社會被分成上下層
把岩層的樣子用在人的群體上：社會或組織被分成上下幾層，上面的人資源多，下面的人機會少，而且層跟層之間很難跨。這是理解上的比喻，不是在主張這個意思在歷史上比較晚出現。
adjective · C1
Describing a society or group that is divided into separate classes or levels, so that some people sit above others in money, power or status.
階級分明的
adjective · C1
Describing rock, earth or similar material that has formed in visible layers lying one on top of another.
成層的（岩石、土層）
adjective · C2
Divided into separate layers, levels or bands so that each one can be treated on its own — used of samples, data, prices, markets and similar things.
分層的／分組的