Flashback allows an instant or sorcery card to be cast from your graveyard for its flashback cost. After a spell is cast this way, it's exiled when it leaves the stack instead of returning to the graveyard.
Kess, Dissident Mage offers a similar strategy by casting spells from the graveyard, while Secrets of Strixhaven brought flashback back through Lorehold cards such as Molten Note. Discard and self-mill are natural ways to stock the graveyard with spells worth replaying.
