Typically, the adventures of a particular Link are encompassed in a single era. An era may also refer to notable time periods in the series' backstory. In Hyrule Historia, eras are hierarchical (one era can have eras within it).
List of Eras
The following is an account of which events occur in which eras, and which published media they are mentioned in.
Hyrule Historia also names the Adult Era and Child Era which correspond to all of the Adult Link Timeline and Child Link Timeline, respectively. There is no such era named for the Fallen Hero Timeline.