Exemplar is an eternal format that encompasses Eighth Edition and forward (the same as Modern). The defining restriction for deckbuilding is that you can only build your deck out of cards that were once in a standard format together. For example, your deck can contain Archangel Avacyn with either Hangarback Walker or Walking Ballista, but not both, because Hangarback Walker and Walking Ballista were never in the same standard format together.

This means that you will get to see many of the great standard decks battling against each other, but tuned to beat a meta filled with such archetypes. So UB Faeries might play Faerie Macabre in its sideboard because it can answer Unburial Rites or Goryo's Vengeance, even though it wouldn't make much sense its native Time Spiral-Lorwyn standard.

Here is a list of all of the eras:

The banned list consists of any cards that were ever banned during their tenure in standard: