A Saga is a prose narrative, typically concerning a family over many generations.
The original sagas come from Iceland, and generally date to the medieval period. They have topics such as great battles, expeditions and family feuds, but they also have more mundane topics, such as the Saga of Burnt Njáll, which concerns a lawyer.
Sagas went largely unheard of in England until the Victorian age, and it is around that time the word saga enters English.
The word itself means much the same in Icelandic – a story. Though is more general, and can also mean a history. It has its origins in proto-germanic: *sagǭ meaning a story. This gives us also the German sage and Luxembourgish so, as well as the obsolete English word saw, meaning something spoken, such as Old Saw.