Eras

In chronology, an era is the highest level for the organization of the measurement of time. A calendar era indicates a span of many years which are numbered beginning at a specific reference date (epoch), which often marks the origin of a political state or cosmology, dynasty, ruler, the birth of a leader, or another significant historical or mythological event

An era is a commonly used word for long period of time. In Star Wars it refers to the durration in which a period of galactic events ocur.