stratification

Short definition from Wiktionary

Noun

1. 1
   The process leading to the formation or deposition of layers, especially of sedimentary rocks.
2. 2
   A layering of musical texture.
3. 3
   The vertical layering of vegetation in a forest.
4. 4
   Society's categorization of people into socioeconomic strata.
5. 5
   The process of treating seeds to simulate natural conditions that the seeds must experience before germination can occur, often involving exposure to cold.
6. 6
   A classification or arrangement of things into different categories or groups.