Short answers, pulled from the story.
Gefjon is a Norse goddess associated with ploughing, the Danish island of Zealand, foreknowledge, and virginity. She is attested in the Poetic Edda, the Prose Edda, and Heimskringla, among other sources. Odin defends her in Lokasenna by declaring that she knows the fates of all mankind as well as he does.
King Gylfi of Sweden offered Gefjon as much ploughland as four oxen could turn in a day and night. She transformed her four sons, fathered by a giant in Jotunheim, into oxen, hitched them to a plough, and cut so deeply that the land was uprooted. The oxen dragged it westward into the sea, where Gefjon set it down and named it Zealand.
The name Gefjon is generally interpreted to mean "the giving one" or "she who gives prosperity or happiness." The element Gef- is related to Gefn, one of the names for the goddess Freyja. Both names are connected to the Matron groups known as the Alagabiae or Ollogabiae.
The Gefjon Fountain is a sculpture by Anders Bundgaard, completed in 1908, depicting Gefjon driving her ox sons as they haul a plough. It stands in Copenhagen on the island of Zealand, the very land the myth says Gefjon carved from Sweden.
Several scholars have proposed a connection. Britt-Mari Nasstrom argued Gefjun is another aspect of Freyja. Hilda Ellis Davidson described her as "one aspect of a once powerful goddess of the north" represented in myths as either Frigg or Freyja. Rudolf Simek was more cautious, noting that even without full identification, Gefjon qualifies as a fertility and protective goddess based on the meaning of her name.
Scholar Frank Battaglia identified five passages in Beowulf, at lines 49, 362, 515, 1394, and 1690, where the word geofon, a poetic epithet for the sea, may encode references to Gefjon. The same root word appears in the Old Saxon poem Heliand. Richard North also proposed that geofon, Gefjun, and Freyja's name Gefn may all descend from a common proto-Germanic goddess.