A saga was a type of ancient literature that told the stories of heroes. Sagas were a part of Klingon literature. (DS9: "The Way of the Warrior", "You Are Cordially Invited")
In 2372, while conversing with Miles O'Brien, Worf recalled rescuing Captain Jean-Luc Picard from the Borg. While O'Brien remembered feeling as though they might not succeed, Worf disagreed; "I never doubted the outcome. We were like warriors from the ancient sagas. There was nothing we could not do." (DS9: "The Way of the Warrior")
In 2373, upon hearing Zahir's tale of landing on a creature they initially mistook for a moon, Kathryn Janeway was confused what point he was making, saying she could "use your help in sifting through that last colourful saga". (VOY: "Darkling")
In 2374, Jadzia Dax became distracted while telling the story of all the women in Sirella's family, prompting Sirella to comment, "You are straying from the saga." Jadzia then explained that she thought it would be helpful to add commentary. She then noted a deviation in the bloodline due to revisionist history, but assured Sirella that she would stick to the official story. An appeased Sirella encouraged her to continue the recitation. (DS9: "You Are Cordially Invited")