In Norse mythology, the god Rig was travelling and happened upon a farm owned by Ái and his wife, Edda ("great grandmother"). They offered Rig shelter and a low quality meal. He slept between the pair at night; Edda gave birth nine months later to a son whom they named Thrall. Thrall grew up strong and ugly. He married Thir and had twelve sons and nine daughters. They became the serfs of Norse society.
The Edda are collections of poetically narrated folk-tales relating to Norse Mythology or Norse heroes.
These are fragmentary parts of a (presumably) much larger scaldic tradition of oral narration which has been written down by scholars prior to the tales being lost absolutely.
There are a number of theories concerning the origins of the word edda. One theory holds that it means "great-grandmother". Another theory holds that edda means "poetics". A third is that it means "the book of Oddi", Oddi being the place where Snorri Sturluson was educated.
There are two Eddas: