Periodization

Periodization is the attempt to categorize or divide time into discrete named blocks. The result is a descriptive abstraction that provides a useful handle on periods of time with relatively stable characteristics. Most sciences that engage the history of some particular object find it helpful to utilize a system of periodization. All of these periods are retrospectively defined, and therefore only valuable to the extent that they aid critical analysis and convenient description. Historical periods are limited by generally agreed-upon temporal and geographical boundaries. Periodization from the sciences includes the geologic Cretaceous or Jurassic periods, while examples from human history include the Modern and Medieval periods. This article uses periods from European human history to elaborate the problem of periodization.
See more at Wikipedia.org...