Historical periods refer to the divisions of time in which events are grouped together for study and analysis. The three terms used to describe these periods are ERAS, EPOCHS, and AGES. ERAS are the longest of the three, typically lasting hundreds or thousands of years. EPOCHS are shorter than ERAS, usually lasting tens or hundreds of years. AGES are the shortest of the three, typically lasting only a few years. All three terms are used to describe the various periods of history, allowing us to better understand the development of civilizations and societies over time.