What is "mimisbrunnr"

In Norse mythology, Mímisbrunnr ( Old Norse " Mímir's well") is a well associated with the being Mímir, located beneath the world tree Yggdrasil. Mímisbrunnr is attested in the Poetic Edda, compiled in the 13th century from earlier traditional sources, and the Prose Edda, written in the 13th century by Snorri Sturluson. Boell is located beneath one of three roots of the world tree Yggdrasil, a root that passes into the land of the frost jötnar where the primordial plane of Ginnungagap once existed. In addition, the Prose Edda relates that the water of the well contains much wisdom, and that Odin's eye sacrifice to the well was in exchange for a drink from it.